Hello, I thought I would just make it clear now that this is NOT a guide. It is tips and tricks for Nasus that I have discovered playing with him. The reason this is not a guide is because I don't want to get downvoted heavily if my information is not of use. If my tips and tricks guide is a success I may finish it. That is entirely up to me though on if I finish it or not. Thank you for understanding! Reading further on you are saying that:
1. You understand the basics of Nasus
2. You know that this is not a complete guide
3. That you will explain to me what you think could be improved if I need to instead of just downvoteing for no reason.

Without further ado, lets get on with the tips and tricks!

Pros:
He's an off-tank that can deal tons of damage! :) (If played corectly.)
When farmed, his Siphoning Strike is OP.
He has got a 5 second slow Wither
He has built in lifesteal with his passive, Soul Eater
Slow someone with Wither and they will almost certainly die.
Good at getting away from ganks with Wither and Fury of the Sands.

Cons:
His Siphoning Strike can be countered easily with Morgana's Black Shield or Fiora's Riposte.
If he gets harassed early game when he has no farm he can do barely anything.
Not really much CC for him to use

Tip #1: He can use his Siphoning Strike to kill turrets quickly, and easily.
Yep, you can. Simple really. Just hit Q when attacking turrets and watch huge chunks of health wither away from the turret.
Tip #2: Farm your Q.
If you don't farm this, you are just plain stupid. Last hitting is the key to playing this guy.
Tip #3: Spirit Fire solo top
If solo top and getting harassed at turret, just put down Spirit Fire and oppoenents will walk out of the AoE giving you chance to get farm.
Tip #4: When ganking, use Wither
This will make killing people a lot easier.
Tip #5: Try to get someone to jungle so you can take solo top
Think of all that Q farm you are giving to your partner. Nasus can't mid because he isn't viable for it. PERFECT CHOICE! :D
Tip #6: Ask for blue
You will be able to spam your skills more often and be able to cast Siphoning Strike more often.
Tip #7: Feel free to target anyone
In team fights, people will be busy attacking AD and AP carries. That is your chance to get some kills. Some people have NO idea that Nasus is doing damage. (unless they are smart of course.)

v.1: First Version of this Tips and tricks.

Thanks for taking the time to look at my tips and tricks for my favorite dog Nasus! Have fun using them! :)