The most important part of this build is farming your Q, which is Siphoning Strike. Every last hit against a minion gives you a permanent buff of 3 extra bonus damage for Siphoning Strike and Siphoning Strike ONLY. So if you last hit 50 minions with your Q, you will receive 150 bonus damage for your Q. A Nasus without a farmed Q in this build, is USELESS!!!

For wither, max it out by at least Lv. 15. Wither is a very important part of Nasus's gameplay. Only slow your enemies when the are around half health, and you must have your Ult (R) before you start chasing champions.

Spirit Fire is your crowd control. It does a decent amount of damage and t can also decrease armour against opposing champions for a short while. While farming lane, use your spirit fire to weaken creeps and then use your Q to last hit them. While chasing, cast wither and then spirit fire. This should slow the enemy in the Spirit Fire, doing damage to them, and decreasing armour.
This is where you use your Ult and then Q. This combo should give you the kill.

Fury of the Sands is your Ultimate. People day that buff ultimate are bad and useless. Well, THEY. ARE. ****ING. WROOOOOONNNNGGGG. FotS (Fury of the Sands) give you increased attack range and a WHOLE BUNCHA OTHER GOODIES that are will get pentakills for you.

When the game starts, you have to farm you're Q and not die. At least get 2 kills before you die. When Tank Nasus is shut down early game, it will be very hard to comeback since you won't get as many kills and you would feed the other team. Use Spirit Fire to weaken creeps and then last hit with your Q. And remember, a Nasus with an underfarmed Q, will give the other team Pentakills, which is not good.

With this build Nasus can REALLY go and tank turrets. His Q can do TONS of damage to turrets. This makes it quicker to to take turrets and inhibitor and get the hell outta there. He can also turret dive under some circumstances, like when he is a 3/4 health. NOT AT 400 HEALTH LEFT!!! This means kills are alot easier to get.

Nasus can be a great player on the field. But, you need smarticle particles to win. So here are some rules to playing Nasus:

1. Never go into fights when you are low in early game. This will make you builds a lot harder to make.
2. Never get cocky. If you start playing around and trying to get kills instead of turrets, you will lose. Never forget that the main goal of the game is to win.
3. Farm the Q. Always. Farm. The. Q.
4. Do not go into 1 v 3 fights unless they are low and you have you Ult OR you are accompanied with a decent teammate.
5. Your combo is E or W,R,Q,Q,Q.

Nasus was my first main and has been my main since. Well, considering I've been playing him for 1-3 months, wait, nevermind. Anyways. My best games with him are 15-4-9, 8-0-10, and ( a more sloppy game), 13-8-17. This has been my first guide and I hope I helped you with plating Nasus!