Hey guys! Just joined and this is my first guide. Will definitely not be the best and WILL be subject to change! It's gonna be a little iffy and there won't be much in it until time passes. Hopefully later on it'll be a much more decorated guide and such.
So a little more about me with the game: As of 11/5/2013, I have only been playing League of Legends for about 2 and a half years. Ever since I have loved the game, and probably like many others I started out with Ashe. I've always instalocked and demanded top lane. Lol. I've grew a habit of always wanting top or support or else I would feel as if I would throw the game. About a month into the game, I've also grew love towards tanks and support. My first tank was Volibear and my first support was Nami. Then I started to mess around with champions like Nasus, Renekton, Vi, Fizz, Ezreal, Gnar, and Ahri which all became my favorites.

Pros:
-When heavily farmed, Nasus will almost have no counters.
-Naturally tanky
-Wither is amazingly great for team fights or chasing
-One of the best lane pushers
-Surprisingly easy to use!
-Built in life steal for sustain

Cons:
-Easily kited
-Not the best early game
-Only one target CC
-Hard to farm if matched up against a ranged champion
-Doesn't have a legit damage source unless heavily farmed with Siphoning Strike (Q)
-HAVE to farm to do damage

Now that all that has been said, lets take a look at why I choose these Summoner spells with some Q&A:

Q: Ignite?
A: I would only choose ignite for more kill potential in lane. As for me, I wouldn't choose it. Early game you should ask your jungler for a few ganks to get you going so you wouldn't really be needing ignite. (You're more focused on farming anyways.)

Q: Ghost?
A: Ghost is okay because Nasus is a tendency to get kited easily. Even when you are using your ultimate, people will still attempt to kill you and kite you as Nasus.
I feel as if Ghost isn't really needed because you have Wither (W) which slows the enemy tremendously.

Q: Teleport?
A: Teleport is a must for Nasus in my opinion. You NEED to get to lane faster for more farm. Let me elaborate. You're not having the best early game, use teleport to get to lane. You need to back, use teleport to get to lane.

Q: Flash?
A? Flash should be a must needed for many summoners. It allows good get away and good engagement. I prefer flash over ghost because Nasus doesn't have a gap closer and flashing over walls is a great way to get away.

Q: Smite?
A: Only if you're jungling. Which I don't recommend on Nasus because he NEEDS to farm. He'll get more farm from a lane than jungle and assists. (Or kills if you ks while you gank.) Well, average 16 minions is a kill (~300 gold). Farming on Nasus is more beneficial to me.

I wouldn't recommend any other summoner spells besides these that have been explained.

The best part. Nasus is a champion of farming AND farm is a necessity for Nasus. If you don't enjoy farming, Nasus is probably not the champion for you. You need much patience farming with Nasus. Besides that, if you have a lot of farm you will turn into a hyper carry. Try your best and last hit the minions with Siphoning Strike. Siphoning Strike also resets your auto attack so it really isn't a hassle farming.

It could be difficult to farm though. If you are matched up against a ranged champion you will feel as if your progress into late game is slow and/or failing.

There is a few things that should come to mind when choosing Nasus (draft pick):
1. Will I be able to farm efficiently?
2. How great will the harass be in my lane?
3. How much Crowd Control do I get from my team?

I believe that Nasus is a great pick any time no matter the match up. Because later in game he will almost lose all of his counters. He becomes THE counter to almost any enemy champion, possibly all, in late game. But his early game is very fragile and without caution he can die a lot. You need to avoid the death timer and use what that time could be as farming time.

Believe it or not, Nasus will have a VERY HUGE impact in team fights and the outcome of a game. Why is this? His Whither and Spirit Fire abilities: Whither will greatly slow an enemy and Spirit Fire will decrease resistances. Nasus is a naturally built tank and has the potential to shut down the enemy teams main source of damage without it being a big threat to him.
Not only that, Nasus shouldn't just go into a fight if his team won't be there to help him. He needs all the help from his team because he doesn't have a many sources of damage (only his Q!).
Remember, teamwork IS OP. So if you're playing as a Nasus, don't always sit and farm; cause we all know we want our Siphoning Strike to be as strong as it can be. If there is a team fight or any fights near you, please do so and join it. They need you to help the team.

Since I just made this guide everything is subject to change: runes, masteries and item builds while I continue on to using Nasus. Not only those, but I will add more builds! Such as a jungle build and guide, full on tank Nasus, or straight AD carry Nasus! I will also continue to work on item buy order for some relief on building and some situational items. (I.E. Ninja Tabi if the main source of damage on the enemy team is AD.)

11/5/2013 - The birth of this guide :D

7/30/2014 - Huge remake.

11/20/2013 - A little more editing and updating on my bio.