Farming Nasus's Q (Siphoning Strike)
Nasus's Q is a very important part of tank nasus. Once you get your warmogs you can farm better.Make sure you last hit minions with it.A way of knowing when to Q is by clicking on the minion and see if they have low health enough to kill them with siphoning strike.You could also lower down they HP a little by using Spirit fire.
Farming with Nasus's E (Spirit fire)
Spirit fire is a AoE type of move.Spirit fire is very good at farming.Always make sure to hit the largest area where minions are.This will help also gaining you stacks with Warmogs.This will also help with harrasing enemies.
Tanking with Nasus
Don't be afraid to start a team fight.You are the tank.Don't be mad if you die a lot.Just help your team out.When starting a team fight always start with spirit fire.Do not wither yet.Siphoning Strike the melee champions.Once at least 3 are dead wither the melee.If the melees are dead then go for the ranged.Careful with people who have madreds.Target them first so they don't wreck you up with regular attacks.Also if your about to die use your ulti because it will help your life steal and help you regain hp.
When pushing always have a fighter with you.Casters cant really kill minions so fast.If you get ganked use spirit fire. If your oppenents cannot handle you start to attack.If your opponents decide to go to you still fight them to help your partner escape.Don't forget to use your q in team fights.And remember if they run wither them and then kill them