When last hitting in lane pay attention to which minions are taking damage instead of responding to small health bars

If you also watch which allied minions are being attacked by opposing minions you can sometimes time harassment to pressure opposing champions at the specific times they move in for a last hit. Ideally if you only make 1 attack or spell while they do this then you run away they will be unable to retaliate, and over time they may not be able to last hit at all for lack of HP.