until first back you will want to use your E as a counter farming tool, placing it where the enemy champ will need to go to kill a creep to deny farm or if they go for the minion, take an unnecessary amount of damage, your main focus will be to farm batter than your opponent while slowly chipping their health away until you can take advantage. Be careful when using your Q at early levels because it will drain your mana too fast, then you will not be able to use your E. I recommend going back with about 1300 gold as this allows you to buy a blasting wand, boots, and health pots. If you need to go back before this, pick up boots, and a second doran's ring. this will allow you to sustain in lane due to the mana regen as well as give you a little boost in AP and health. At level 6 you will hit a massive damage spike. if their opponent is around half health all you will need to do is Q,E, then Ult and watch their health drain to 0.