In early game, what you want to do is just farm, and if your opponent starts to poke you, whenever he gets in your range, or there are enough minions grouped up in your E's range, use it to get your passive's shield. If they start to destroy your tower, go on top on them and defend. If they get aggressive and get on top of you, use W on a minion close to you and then E and Q, and if you have ult, use it when they get low, and if possible to assure the kill, use ignite.