My experience?
Start low-powered. The shiny powers - especially Evocation - are VERY powerful, so you don't need to start at the high power levels.
When play starts insist that the rulebook is put away. If people have .pdfs have them close the computer. There will be no looking up rules, arguing rules or saying "but the book says..."
It kills the pace completely and can drag down the action to "well, I want to go ask around the street, but I only have Contacts +1. Maybe you should do it, <player name>, since you have +3?" which is entirely against the spirit of the game.
If you don't know something a player asks about, there's four options:
1) Make something up.
2) Ask them to make it up.
3) Ask them to make it up and reward them with a FP for creativity.
3) Ask them to make it up and pay a FP/make a declaration.
Compel constantly. My suckiest sessions had two or three compels over the course of the session. The greatest had compel after compel, which encouraged players to invoke constantly to be badass and take charge of the story.
Make sure that the characters have a clear goal - individually and/or as a group - that you can use.
Don't be afraid to cheat. Storm Front wouldn't have been as interesting if Harry had just gotten Sells right away, now would it? Use concessions, Fate Point "bribes" and narrative sleight of hand to keep things interesting.
Remember: You WANT the characters to succeed, but you don't have to make it easy for them.
No one likes that.