Laning:
Harras the enemy with your E.When your E's cooldown finish,throw it again.Mana is not a problem unless you trade your enemy.If your mana is lower than the half,throw less E.
Don't use your skills much when farming.Just use your Q if you think you can't kill the minion or use your W for under turret farming.

Fights:
Use your Ultimate actively in fights.Don't focus tanks and don't let enemy to focus you.Focus the ADC if you reach,if you can't try to focus AP Carry.If you get focused,use your Q W R and press Zhonya while your Ultimate opened.Watch them to die! :)