Abilities

Soul Eater(passive)
Nasus drains his foe's spiritual energy, giving him a natural 10/15/20% lifesteal. The lifesteal value increments at levels 1,6, and 11.

This is a great passive, it allows him to jungle(though, it's not worth it to jungle with Nasus; He is an awesome laner:)), to lane for longer periods of time and to get back to pushing turret after a team fight where you would normally have to go back to spawn.

Siphoning Strike
Nasus strikes his foe, dealing damage and increasing the power of his future Siphoning Strikes if he slays his target.
Nasus's next attack will deal an additional 30/50/70/90/110 damage (+). Siphoning Strike permanently gains 3 damage whenever it kills an enemy.

This is an awesome skill. It is going to be your bread and butter early and mid game. It's great for last hitting, and it deals quite a big amount of damage, if used to last hit a lot. Also remember that this kill resets your auto-attack, so it is very important that you don't mash your q button. Press it right after you've made an auto-attack. If you are doing this, you will see a great increase in your damage output (remember to do this against turret too).
I put 1 point in this at level 1 so I can start building up the damage on this spell

Wither
Nasus ages his target, decelerating their movement and attack speeds over 5 seconds.
Nasus ages his target, slowing their movement and attack speed by 35% and reducing it further by 3/6/9/12/15% each second for 5 seconds.

Pretty self-explanatory. A great slow with a decent cooldown. This skill will ensure many kills for your team. It can also be used to slow chasers when trying to escape.
It is very important to notice that it doesn't only slow movement but also attack speed! This is great for throwing on the AD carry in a team fight making them almost useless.
I put a point in this at level 4, so I have the slow for laning and fights in the lanes(it can also save you and your laning partner from a gank) and then I start maxing it from level 12-15, so it can be used for team fights in mid game.

Spirit Fire
Nasus unleashes a delayed spirit flame at a location, dealing damage and reducing the armor of enemies who stand on it.
After a brief delay, the target area becomes desecrated. Enemies in the area have their armor reduced by 20/25/30/35/40 and are dealt 20/34/48/62/76 (+0.2) magic damage each second.

This skill has many uses. It actually has more uses than I can mention, but I will mention some of them; it is a great farming tool when thrown into the middle of a minion wave. This usually keeps the enemies on the lane away from your minions. But there is also the part that says "reduces armor". Now this is the best thing about the spell. At rank 5, it reduces the armor of enemy champions by 40! And since it reduces the armor, it can also go below 0. The AD carries on your team will praise you to the skies when you use this spell in the middle of a team fight!
This is the first spell I max, due to the amazing farming capabilities and the 40 reduced armor. Why only 2 points in it before level 8? Because at level three, this spell deals too much damage to caster minions, and you do not want that, since you are going to lose a lot of last hits that way; You want the minions low hp, so you can go last hit them with you Siphoning Strike, but not too low, so your minions are going to get the kills.
It is important to remember not to spam it. It costs a lot of mana for Nasus, so don't you use it on every single minions wave. Use it if they are pushing, to prevent it. Use it if you need to push a little more. A nice ground rule (Ground rule, as in something you can do if you are still learning Nasus) is to use it when the minion waves with the cannon come. I personally use it, apart from the cases above, every time I am at full mana; another ground rule: If you have full mana, use a spell, unless it is just before something that might turn into a teamfight where you are gonna need all of your mana for success.

ury of The Sands(ultimate)
Nasus unleashes a mighty sandstorm that batters nearby enemies. While the storm rages, he gains additional Health and drains nearby enemies' max health and converts it into bonus damage for the duration of the skill. Nasus becomes empowered in the sandstorm, gaining 300/450/600 health. While the storm rages, he drains 3/4/5 (+0.01)% of nearby enemies' health each second (240 damage max per second) and converts it into bonus attack damage.

This is an extremely nice ultimate. It increases your chance of survival in a teamfight, in increases your damage in team fights and it either makes people run away from you, or focusing you, because they want to take you down, since you suddenly became a major threat. The only thing about this skill is when to use it. Never use it in the start of a team fight, use it when everyone is standing close, so your ultimate will drain hp from more enemy champions. It can also be used when you have lost a lot of health; the bonus damage is great. It is also great for the mid of a teamfight when you are about the 70% of hp. The increased HP actually demoralize the enemies, since it becomes quite har to take you down.
The added bonus damage is quite nice, even when tanking. Combined with Sheen it makes your Siphoning Strike hit very hard. The amount of AD recieved by this spell is 5% of the damage dealt (from the drain). This means that you get 1 AD every time you deal 20 damage with the drain, 10 every time you deal 200 damage. It doesn't seem like a lot, but it is. Especially when around a lot of enemy champions/minions.
Another thing that makes this spell awesome is the duration. It is not just 4-6 seconds as a lot of other ultimates, giving you the upper hand in fights.
I of course, max this skill ASAP.


Skill Order
In this section I intend to explain my skill order, and hopefully answer the questions you might have.
I start off with a point in Siphoning Strike at level 1. I do this because this is the spell with the largest damage output, so it is good for first blood. I also put a point in this, to start building up the damage on this spell as fast as possible.
At level 2 and 3 I put points in Spirit Fire to start pushing. These skill can change who is pushing, and if you are already the one pushing, it just makes it harder for the enemies to try and push.
At level 4 I put a point in Wither since you of course need this slow in case of ganks or fights.
The point in Siphoning Strike at level 5 is to make it easiere to last hit and also increase your damage a bit.
From level 7 to level 10 I max Spirit Firefor maximum damage and armor reduction in the teamfights that usually start a bit after these levels.
After this I just max Wither ASAP (after ultimate of course) to maximize the slow, making it very hard to escape teamfights for your enemies, and to disable those AD carries.
Once Wither is maxed, I put the last points in Siphoning Strike


Runes

I take 3x since Nasus is a tank, and a quite squishy one early game, so he really needs that extra HP.
I take 9x because there is a need of magic resist in every single game, even attack damage champions(most of them) have at least 1 skill that deals magic damage.
I take 9x These runes are excellent on Nasus, since they make Siphoning Strike hit like a truck, and they work against all kinds of champions (tank, ad and ap). If you are having problems with AP nukes, check the "other runes" section.

I take 9x because Nasus runs out of mana all the time, these runes really helps to minimize the amount of trips back to spawn. And there is nothing worse than running out of mana in a team fight. Using these runes also allows for more tanky items, since you don't have to worry about mana regen items.

Not level 30 yet?/buying order
If you are not level 20-30 yet, do not buy any runes. It might be tempting, but don't; it is a waste of IP. Wait until you reach summoner level 20, and then start buying runes. Start out by buying , then , then and at last .

Other Runes

This is a section with other runes that you can you use. I recommend the runes above, but there is not a big problem in using the runes below.

. This is a pretty standard tank rune. Quite good against AD champions, especially when combined with dodge masteries and Ninja Tabi. The reason I don't recommend these, is that I personally prefer the mana regen runes way more. Using these runes might make a big need for mana regen which can solved by buying a Chalice of Harmony. This has to be replaced later, and at that point you might experience a few mana issues. A second reason why I don't take this rune, is that I never have problems with AD champions, so I see no great need for anti-AD runes.
Thanks to Searz for recommending these runes.

since I've lately had a few problems with fed casters, and I extra magic resist is always needed. I take Warding instead of Shielding, since does not give the same amount of magic resist as Mark of Warding before level 15.

Summoner Spells

I take ghost because it allows you to move to the places where the action is happening in no time + it is great to use for chasing and in teamfights so no one can escape the wrath of your ultimate.
In my opinion every tank has to have teleport. It is great for so many purposes. It allows you to save a turret, to push a turret, to go back to spawn and buy items and to quickly help teammates or join a team fight if you happened not to be around.
This are the ones that I use, and that I recommend the most, but the ones below are also valid.
Quite a nice spell. Most people either overrate it or underrate it. It is not the best, but it is nor the worst. Great for laning, and great for turning a teamfight.
A great summoner spell, especially after the buff. This spell should only be used as a slow early game, mid and late game your Wither should be used for this. Mid and late game you should use exhaust as a disable on carries. Use it on the carry that you think are going to do the most damage to your team; do not use it one the carry that is surrounded by 3 of your team members, use it on the Miss Fortune or Ryze standing to the side, getting ready to smack out some damage.

Summoner spells that are ok

A very underrestimated spell. This is great in teamfights, and great when pushing turrets. But remember! Only pick this spell, you have 2-3 AD champs on your team (A part from you). AP champs don't really gain anything from this.
An awesome spell. Great throughout the entire game. It grants you the most important thing in the game. Map awareness. It could be checking for ganks early game, checking dragon, checking baron etc. But it would be better to let a support or someone who is going to specc improved Clairvoyance have it.
Another nice spell. Great for defending a turret when the backdooring Yi is hackin' and slashin' at your turret, giving you and your team enough time to get over there and kill him.
A nice spell, but it is not really important since as long as your ultimate is popped and you've thrown your Spirit Fire, it doesn't really matter if they stun you. They just wasted it on you instead of on the carry. But it might help you out of some sticky situations in early game.
A nice spell, might get you into range of your slow, or save your ***, but i don't really like this spell on most tanks.
Yes. That is right. Revive. No it is not a bad summoner spell. It just useless on most champions. But when playing the tank, it is incredibly important to be with your team at all times! So if you die, your team is basically useless. This allows you to always be tanking. But what makes this spell bad? The eight minute cooldown...

Summoner spells not to pick:

Unless you are jungling, this spell is useless.
You bought mana regen runes, you specced more mana regen, and you want clarity? You are not supposed to spam your spells that much.
Not on a tank. You are not supposed to kill steal your carries' kills. Your job is to make your carries get kills, not take them.

IMPORTANT: If you choose any other summoner spell than the one I recommended, remember to adjust your masteries after that spell, so you can improve it (unless it is Rally of course).



Masteries

For masteries I get 16 in defence for the increased HP, dodge and armor/MR and 14 in utility.

Defensive = 15:

Resistance: I put 3 points in this, increasing my magic resistance by 6. This is a flat amount so this is 6 magic resist at level 1-18. Magic resist is important for a tank, so he doesn't get nuked by casters.

Hardiness: I put 3 points in this, increasing my armor by 6. This is a flat amount so this is 6 armor at level 1-18. Armor is important for a tank, so he doesn't get eaten by AD champions.

Evasion: I put 4 points in this, increasing my dodge chance by 2%. It is a low amount, but it is the best of the defensive talents at this tier, and dodge is never bad for a tank.

Nimbleness: This is quite nice, as you are most likely gonna dodge attacks in teamfights, so the 10% increased movement speed allows you to keep enemies withing range of Fury of the Sands.

Harden Skin: I put a single point in this, blocking 1 physical damage, as there is no need for more points spend in defense, before I can put points into the next tier. The 1 physical damage blocked is decent. It is not, but it is never the less the best option you have.

Veteran's Scars: I put 4 points in this, increasing my health by 48. This is by far the best talent you can get in defense. The 48 hp can be crucial early game and can often be the difference of loosing or winning the battle for first blood.

Utility = 14:

Spatial Accuracy: Reduces the cooldown of Teleport by 5 seconds and reducing the time spend from clicking, till you actually arrive at the destination. The reduces delay can sometimes be crucial.

Haste: A great talent. Not only does it increase the movement speed of Ghost by 8%, but it also increase the duration, by 1,5 second. This is one of the best summoner spell improvements.

Good Hands: I put 3 points in this, reducing the time dead by 10%. You might think that the 3 points in reduced time dead (Good Hands), is a waste of mastery points, but think about it. You are going to a die as a tank, I am not denying that, the amounts of deaths will vary, but you are going to die. Without you, the tank, your team is incapable of winning a team fight and in some cases they can't protect a turret, because they are 4-5 attacking it, and they have to fall back and let the turret be destroyed, so the less time you are dead, the less chance of you losing your game :).

Awareness: I put 4 points into this, increasing my experience gain my 5%. This is great, since it allow me to reach higher levels faster, possibly winning a lane fight, because we are level 6 and they are level 5. This can also be a turning point for midgame teamfights or reaching level 11 fast, so you can kill Baron.

Utility Mastery: I put 2 point in this, increasing the duration of neutral buffs (Golem buff, lizard buff and baron buff) by 30%. This is great for Nasus, since all buff are good for him, and he needs the Golem buff, so it is great if the duration is increased bt 30%. It is also important to notice that it is not just lizard and golem, but Baron buff too, giving your team a major advantage in teamfigths for a longer period.

Meditation: I put my last 3 points in this, increasing my MP/5 by 5. This is a great mastery for Nasus, since he is so mana hungry, and the best part is that it is flat Mana Regen, allowing for more Siphoning Strike and Spirit Fire spamming early game.

Why these masteries?