Stack as much Q as u can, it's you'r main damage :)

U are better than you'r opponent beacus u have passive life steal, more healt, bigger damage,..
Make sure when u get into fight with you'r opponent to use E and be in the circle of skill, opponent's armor is reduced, u will get easy kill. IMPORTANT
And if u can make him come to you'r minion's and that will be you'r advantage.

Stack as much Q as u can...

U need to play defensive, and let enemy's minion's come to you'r tower, but not to close or you'r tower will hit and kill them, you wont get farm and stack Q.
That way you can't be killed, if they dive you, u will at least get 1 kill and survive, and with Nasus's passive, hitting minion's will gain you health :)

Again, Stack as much Q as you can ._.

First of all u must change you'r summoner's spell's from Flash and Barrier to Flash and Smite.
When you spawn, go to blue and wait 1:50, get blue, go to wolf's, witches, red, golem's.
You should be about 3 lvl, gank top and mid.

Enjoy