It literally is all about the Q and stacks. The two biggest and best tips to give a Nasus player: Earn those stacks. And know when it's time to join your team to put them to use.
Cooldown reduction is Nasus's core stat. He wants that 40%(or 45%) CDR so his Q is up as much as possible. More Q's more often = more stacks, faster. Stacks = win.
If you go to Q a minion and get hit a bunch, that's an e v e n trade. Most champs would consider a trade where they take damage and dealt none a bad trade. Nasus doesn't care he has built in life steal and sustain. He wants the stack. He gets the stack it's good for him. You want to rush cooldown too. If you can't get Sheen first back get Boots of Lucidity.
Prioritize Q'ing Canon creeps too, make sure you Q Turrets too. You wanna go Q, W, E max, leveling up your ult when you can. You can hold your ult during a fight to "turn it around" but sometimes its best to pop asap and use the AOE and Q reduction to max benefit. Approach Velocity is great on him, and I prefer Conq keystone.
Ghost/Tp are good sums.
Either split push and then use Tp to join your team. Or fight with your team and Tp to a side lane to create the most pressure.
Stacks.........all about them stacks.