First you go in with e, then q to clear cs or deal damage to your opponent. Next depending on how much damage you are able to do at that point you can e again past you enemy top laner to maybe get a kill or back if you want to play safe. Use your ult when you feel like you are about to die and you think you can kill the person your chasing. You can also ult when your getting chased and you dont want to end up feeding your opponent.