Her passive is called deadly cadence because it allows her to spam spells better then any other champion expecially in early game. From level 1 your goal might be to harrass with your Q every chance you get while farming creeps with it, remember to time your poisons right to farm better. At level 2 you should be able to spam your E after poisening them with Q. By level 3, and on, your W should be your initiating spell, slowing them down, hitting with E if you can, and hitting with Q if poison is about to come off of your enemy, of course spamming your E every chance you get. By level 6 with your ult, you can try to pick off any champ you can, or in team fight try to get 3 or more to help your team a lot more then most champs can with their ult, of course trying to do it when they are looking at you, it mostly works at the beginning when they are all trying to initiate.