I can not stress enough that you NEED to farm Q!!! unless you are going AP Nasus you need to to be a effective champ. If you don't hit 200 stacks by 20 mins then your doing everything wrong! If you see yourself fall behind then farm jungle wolves or switch lanes with someone who has already took tower. If you hit 400 stacks by 20 then your doing awesome and your set up to be a beast late game. If your at 800 stacks and you have a bloodthirster then you can solo baron if you use your ult and you have enough mana. Q farming will make or break this champ.

The thing about nasus is that his early game SUCKS!!!! Dont go for kills, go for harass with your Q if they harass you. Soon you'll out trade them and if they get low and go in on you THEN you can kill. Dont go for the kill or go for the harass early only react. Nasus scales better from farm then from kills unlike almost every other champ out there and remember that! On the other hand take free kills.

You have a really hard time early with mana if you spam spells. I had so much trouble I even tried going for a chalice of the harmony! When you lane don't use your E unless you are hard pushing when they go back or if you want to go for champ harass. Save your W until they go all in or your ganked. WATCH MANA! You can run out of mana really fast if your not careful.

Pros-

AMAZING LATE GAME
Scale infinity
Is a good team fighter
Is not very popular right now ( not banned often )

Cons

Can be kited easy
Can be escaped easy
Bad early game
Needs farm