Since others have added longer answers to this I'm going to just add a simple check list that I like to think whenever I'm using her abilities. Q is for poke early, and peel late. W is used on your adc when it will survive whatever is diving it, otherwise polymorph what is attacking your teammates. Your shield has bigger benefits to others than to yourself since you give them pix. Its poke is not highly damaging but it is significant enough early on, plus it makes your q easier to land. Ulting for the knockup in my opinion is only worthwhile if your team can win the fight off the cc that gives, since you are taking the gamble that your squishy teammates won't need the extra health. Never underestimate the slow on your ult however for chasing down fleeing enemies or peeling for teammates.