dont waste all your mana on minions but use your q occasionally to poke enemy and kill large groups of minions. to do massive damage and get kills, poke by using your e,w, then q. do this until the enemy has farely low health then do the same thing and when he flashes away finish with your ult. dont do this too often early game because it will drain a lot of mana. go back as frequently as possible when you have lots of money but make sure the enemy goes back too so do lots of damage to scare him off. or if not tell your jungler to cover for you. do this later on in the game not too early