I'm tomo7 I've been playing Nasus for 3 seasons now. I also have one of the top singed guides on mobafire so check it out if you want.

I have a youtube channel Tomo7 where i am planning to upload some nasus content soon, mainly featuring all of the matchups and how to play with a feeding team as nasus, this will be coming very soon!!!

Nasus is a good champion to learn the basics of climbing.

1. He teaches you restraint, due to his horrible early game you shouldn't be harrasing your lane opponent, or anything else, don't auto attack early unless it is a q empowered auto. just last hit with q and your fine.
2. He teaches you the importance of farm, for the first 20 minutes of a game all Nasus has to do is focus on farm, he doesn't need to roam (although Teleport ganks can help in certain moments, but nasus's teleport ganks are kind of rubbish) Nasus should generally be living on the topside of the map.
3. He teaches you how to play safe. Most junglers love living top side when a Nasus is in the game so you always have to be careful.

Need more proof? heres a video of what happens if nasus is given a free lane: Play Video

This chapter covers the early game items for Nasus.
The best stats for Nasus in the early lane phase are: cool down reduction, tank stats, health, mana and sustain. So items like Glacial Shroud, Spectre's Cowl, Sheen, Ancient Coin and Corrupting Potion are all good items to build early on Nasus, however its all matchup dependant.
For starting items there are 4 good starts. Cloth Armor with 4 Health Potion's, Corrupting Potion, Doran's Shield 1 Health Potion and Ancient Coin with a Refillable Potion.
Go Cloth Armor verse ad caster champion like Fiora, Darius and Jayce.
Go Corrupting Potion if you are verse a ap champion who will poke you out of lane.
Go Doran's Shield verse auto attack based champions like Tryndamere or Master Yi.
Go Ancient Coin verse champions with low kill pressure on you early like Malphite or Maokai

For summoner spells I would suggest the following:

Flash A very safe summoner for Nasus can help him secure kills he would otherwise be unable to get, helps to escape ganks and is overall a great summoner spell on any champion.

Teleport Another very safe summoner for Nasus allows him to get back to lane faster to stack his Siphoning Strike

Ghost is another option for Nasus however it is not as safe as Flash. taking Ghost in top lane is pretty much begging the enemy jungler to come and gank you. The only time I would ever say Ghost is good on Nasus is if the enemy team lack crowd control effects.

He is a easy champion to play which you can be consistently good on. Compare that to champions like Yasuo, Riven or Lee Sin you have to be *always* good and preform to the champions full potential to win, with Nasus you don't need to land fancy skill shots, you don't need to land crazy combos and you don't need to do any animation canceling. Nasus is a basic champion, with a basic kit, with a basic play style.

Nasus may seem boring but he is damn effective for low elo climbing.

Passive: Soul Eater
Passive type: permanent stat buff.
Nasus gains 10/15/20 (at levels 1,7,13) bonus life steal.
A basic passive which allows nasus to sustain in fights or in lane, very helpful to survive.


Q: Siphoning Strike
Cooldown: 8/7/6/5/4
Mana cost: 20 at all ranks.
Nasus empowers his next auto attack to deal a low flat amount of damage (30/50/70/90/110) which scales with 100% of his attack damage. It also scales off how many stacks he has acquired.
Apon killing a minion, monster, champion, clone, summon, tower, dragon, baron, tibbers, tentacle, barrel, teemo shroom and yorick ghouls he gains stacks.
+3 stacks for minions, small jungle creeps, and most summoned item in game (zz'rot portal void spawn, shaco box, malzahar voidlings, zyra plant... etc, only thing not stackable is yoricks w and jungle plants)
+6 stacks for champions, clones, towers, dragons, barons, large jungle creeps, tibbers and the maiden.
This q infinitely stacks which makes Nasus a good late game champion, in a 1v1 situation because it is a single target/empowered auto attack.

This also resets nasus's auto attack timer.
This ability is why nasus works well with Sheen its overall more damage.

W: Wither
Cooldown: 15/14/13/12/11
Mana cost: 80 at all ranks.
Nasus ages target champion over 5 seconds, slowing their Movement Speed by 35%, increasing to 47/59/71/83/95% over the duration. The target's Attack Speed is reduced by half the amount from 17.5% too 23.5, 29.5, 35.5, 41.5, 47.5% over the duration.

Wither is a very powerful spell when casted on an adc who relies on attack speed, and also is good on whoever is harassing your backline

E: Spirit Fire
Cooldown: 12 seconds
Mana cost: 70/85/100/115/130
Nasus creates a ring of fire dealing 55,95,135,175,215 (+ 60% AP) magic damage on impact and deals 11/19/27/35/43 (1/5 of the impacts damage) per second. Spirit Fire also reduces the armor of whoever is inside by 20/25/30/35/40
In teamfights drop this on whoever is closest to decrease the targets armor increasing you and your ad team mates damage to them.
Do not use this on baron/dragon it doesn't decrease its armor, it is just a mana dump for no reason.

R: Fury of the Sands
Cooldown: 120 seconds
Mana cost: 100 at all ranks.
Nasus empowers himself for 15 seconds gaining bonus attack range, 300/450/600 health, 15/35/55 armor, magic resist and 1/2/3 armor and magic resist over the duration of Fury of the Sands (up to 15/30/45 of each stat)
While Fury of the Sands is active Nasus deals 3/4/5% (+ 1% per 100 AP) of target's maximum health.

Use this at the start of a fight you will be tankeir and harder to kill, NEVER use this at last second, Fury of the Sands is not meant to save your life, it is meant for the combat stats over time.

Overall Nasus's kit promotes farming, being tanky and annoying and splitpushing.

Items

Trinity Force vs Iceborn Gauntlet In most games I would say trinity is better than ibg because of 2 factors: 1. trinity gives more overall stats. and 2. slows don't stack so when you Wither some body the ice born slow is basically useless. However I would say Iceborn Gauntlet is better verse all ad teams. sure you may say ice born is cheaper but once you get it, it pushes the minion wave by itself because of the items passive, which would deny you q stacks. I would not recommend rushing either of these items, buy a defensive item/component first to survive the lane phase.

Dead Man's Plate vs Sunfire Aegis Dead mans is the best option here, when it is at 100 stacks it makes your next auto attack deal 100 bonus physical damage (which proc's off q) same as before buy both vs all ad teams.

Spirit Visage vs Banshee's Veil Visage is a better choice if the enemy team have 1-2 ability power threats, it increases your passive healing and corrupting/refillable potion healing, this does not increase the amount of health Nasus's ultimate gives.

Runes

Marks: ad vs lethality vs attack speed.
Attack damage marks only help Nasus between level 1-4 at that point you will have enough stacks to be safe last hitting.
Lethality marks ALWAYS scale, increases Nasus's late game damage, but make his early lane phase rough.
Attack speed marks allow nasus to use his passive more and speed up the animation of his q auto attack, they make last hitting under tower easier, but fall off when he gets trinity force.
The best option I recommend are taking ad reds because you need to have some strength in the early game as nasus.

Gylphs:
Cooldown reduction vs magic resist vs magic resist per level.
Cooldown reduction blues make nasus's early game easier, more cdr more stacks and also help towards his main goal of getting 45% cooldown reduction as fast as possible.
standard magic resist blues are good verse ranged ap toplaners like Kayle or champions that stack alot of magic pen early like Rumble
Magic resist per level are good verse mostly ap teams eg if the enemy have a Rumble top, Elise jungle and a Ahri mid.
Cooldown reduction blues are the best option, however take either of the magic resist blues in situations where they are needed.

Seals:
Armor vs health per level.
Armor seals help nasus in the early game to farm easier and not get poked out as easily vs ad matchups.
Health per level seals scale to late game, help deal with ap top laners and are the best late game seal for nasus.
This one is up to you to decide, if you need the early armor or need the extra health for late game.

Quints:
Armor vs ad
Armor quints help nasus in the early game and in the mid game.
Ad quints helps him secure early farm verse ranged matchups.
Armor quints are always the best choice on Nasus because of his weak lane phase he needs suitability

Masteries:
Wanderer vs Savagery. take Savagery to help your early game to allow you to last hit under tower easily and take Wanderer verse ranged matchups who will poke you out of lane easily if you go the sustain nasus build.

Secret Stash vs Assassin . another early game verse late game one, Assassin is the best for Nasus because he is sitting in toplane/botlane by himself for most of the game, it increases his damage by 2% which can secure kills he wouldn't of got without it.

Merciless vs Meditation . take Merciless it increases Nasus's q's damage by 5% when the enemy are below 40% health.

Greenfather's Gift vs Bandit vs Dangerous Game . Dangerous Game is the safer option here for when you start grouping with your team, however Bandit is the best one verse ranged matchups where Nasus will get zoned from farm Jayce

Precision vs Intelligence . this one is brain dead simple, you take Intelligence to increase your cdr cap to have Nasus's q and w up more often.

Stormraider's Surge vs Thunderlord's Decree . no questions asked, go Stormraider's Surge it removes the counter play to nasus in the late game, kiting him.

Recovery vs Unyielding . because Unyielding increases the resistances Nasus gets from his ultimate it is a must take.

Explorer vs Tough Skin vs Siegemaster . the only 2 I would ever say take are Tough Skin and Siegemaster with how common it is for junglers to dive toplane (even more if your playing Nasus) I would say Siegemaster is better if the enemy have a diving jungler like Lee Sin Xin Zhao Rek'Sai. other than that take Tough Skin .

Runic Armor vs Veteran's Scars . take Runic Armor it increases your potion healing and your passive life steal. Veteran's Scars is possibly one of the worst masteries in the game after they nerfed it in season 6.

Insight vs Perseverance vs Fearless . take Insight if you are taking Ghost on Nasus if you are not taking Ghost just use Fearless since it scales well. never go Perseverance this mastery is only good on 2 champions Dr. Mundo and Volibear because their kits include crazy regen.

Currently there is 2 keystones nasus works the best with... Stormraider's Surge and Grasp of the Undying

Stormraider's Surge is by far the best keystone for Nasus since nasus can proc the keystone really easily in mid to late game.

Grasp of the Undying is good into melee bruiser matchups like Fiora and Olaf

The other keystones don't really work that well with Nasus Deathfire Touch had its ad ratio nerfed recently (patch 7.5) Warlord's Bloodlust is not worth taking on any champion, Nasus can't really use Fervor of Battle that well. He sucks with Thunderlord's Decree cannot proc Courage of the Colossus and doesn't work that well with Bond of Stone

Trinity Force Build
Trinity force is one of the best items for nasus, it offers everything a nasus wants. flat ad, more damage on q, health and mana, cooldown reduction, move speed and attack speed, Trinity Force I would say is ALMOST core but in some matchups Nasus has to build ice born instead ( Jayce , Darius) to survive the lane phase. However rushing trinity force first item is always risky since nasus will be very squishy, he will do alot of damage however. It is recommended to rush a defensive item first like Frozen Heart, Spirit Visage or buying the cooldown reduction component of those items ( Glacial Shroud Kindlegem) this will make nasus hit his powerspike of 45% cdr very fast.

The mixed CDR build

This build is a very good early nasus build verse hybird champions or verse a mixed top/jungler. it rushes towards nasus's powerspike of 45% cooldown reduction and is a perfect opening into buying a Iceborn Gauntlet and Spirit Visage this build works best against tanks. However with this build you go other the cdr cap easily.

The Sustain Build
The sustain build is a build I have developed recently to get past poke lanes like Jayce and Quinn it involves stacking early health regen, in the early game sustain is always better than armor/magic resist. With this build you start Doran's Shield to help the early game, once your forced to base after most likely being poked out of lane rush 2 Rejuvenation Bead's this helps the early game verse these poke champions, next you want to rush Raptor Cloak and Boots this helps nasus get back to lane faster, with this build you can farm 2 minion waves, base then be back in time for the next minion wave when it hits your tower. This build gives up nasus's early game for sustain to not feed the toplaner.

This image shows the basics to nasus stack milestones for the time stamp, it is a very good image to remember.

Video Done by Scaling Q (aka. Tekl) covering how to stack with nasus during the lane phase: Play Video
This is where alot of new nasus players struggle, its just knowing nasus's early q damage. at level 1 it is basically the exact same as nasus's basic auto attack. A trick you can do on nasus on the first minion wave is auto attack kill the 1st melee minion, Q reset the 2nd and auto attack kill the 3rd. However if you do this expect to get zoned from the 3 caster minions.

On Nasus you want to start with Siphoning Strike first to get your first few stacks at level 1, in most games you will only get 6 stacks off the first wave, anything more just shows that your laner is being passive.
Second you generally have to take Wither because of a aggressive top laner or jungler will punish you between level 1v2 so you need to have a way to get them off you, Nasus not taking Wither second is extremely punishable and is where most new Nasus players do bad, they take Spirit Fire shove the wave and use all their mana.
Third should be Siphoning Strike to lower its cooldown, you don't need to get Spirit Fire until level 4 because of how low of a impact it has and the high mana cost, using this spell to harras early is useless, you are just going to push the wave which will lead you into over extending as Nasus and it is a huge mana dump early unless you have a dorans ring.

For skill max Go rqew. your ultimate first because it gives increased health and resistances, your q second because it lowers the cooldown allowing you to acquire more stacks and increases the base damage slightly, your e third because its strongest point in the game is in the mid game before midlaners/adcs start buying armor, this also increases the base damage and the mana cost heavily, but it allows Nasus to waveclear faster in a mid game splitpush. Wither last because it scales better after level 13 when nasus starts to group/teamfight.

Nasus's main goal for the first 30 minutes is too gather as much farm as possible stack q then kill things later. When playing Nasus your attitude should be: Keep Calm And Farm. oh the riven is harrasing you out of lane? keep calm and farm you will outscale.
Don't sit there typing to your team telling them how bad they are playing, they already know they are bad so you don't need to tell them.

JUST KEEP CALM AND FARM

Now alot of people say Nasus is a pure late game champion but really his late game over rated, its his mid game that is the best. in late game Nasus will just get kited by all of the high mobility champions that can run circles around him, which leaves Nasus to attack the tanks. Nasus is not an assassin he shouldn't be jumping in trying to one shot a adc. Nasus is a tank that can peel for his team with Wither. A big mistake alot of nasus players make is the Wither the wrong person, they think they should always be Withering the adc, that is wrong, Wither the closest target to your team (unless it is an Olaf)