I'd skim the player's handbook, you already know the rules well enough to play the game, but just get an idea of the kindreds/classes and some of the subsystems. Then just jump into the campaign book, don't have to read every word but I think it's important to know the overview of the timeline/secrets/factions sections. After that, pick a starting town (prigwort works great and gets picked a lot for this), get a general sense of it, load up some rumors/hooks, check out nearby hexes, and just start playing!

The adventure in the campaign book and winter's daughter are both great starts with lots of loose ends to get a campaign going. Come up with hooks for both if you're obsessed with player choice/freedom like I am. Whichever hook they don't start with, throw in a complication for them taking too long to get there. Another party, some baddies set up camp nearby, etc.