1. You max E -> Q -> W. E because the cdr and the damage gets higher, not to mention the slow is like 50% and its your bread and butter. Like, there's absolutely no reason to not max E always. It's an escape, untargetable, and has short cd. Literally no contest. Q because it's a god damned gap closer and it also has cdr. You seriously should not be maxing W lol that's awful.
2. You 150% always rush sheen. I usually get a 2nd dorans ring if I'm losing or I grab a flask in unfavorable match ups. Sheen rush always then build dfg if ahead or Lich Bane if behind. The rest depends on how the game is going. DFG helps because you seriously need to get rid of their banshee's.
Start with W, E, then Q (Unless you are aggressive, then switch Q and E for the first 3 levels) then max your E first because it costs a lot of mana. W is maxed 2nd because it adds insane DoT, Q is saved for last because although it lowers cooldowns, the W power is better.
On my first back I always try to get sheen but if I can't I go double dorans, some wards and pots. I rush lichbane unless I'm against someone who counters fizz, then I go zhonya's.
Also if you know who you're playing against in lane, make the smart call of either going Doran's/2HpPots, Flask/3HpPots, or Cloth/5hp pots (I think) so then you don't get destroyed early.
In late game I end up with LichBane, Zhonya's, Rabadon's, Void staff, and other stuff depending on the situation.