i would do a lot of BB sight reading when you shed. get Tommy Igoe's GE 2.0/1.0, Steve Houghton's books (anthology, studio/ big band) & then search the internet for big band charts to match up w/ youtube or grooveshark tunes. check out Tommy Igoes approach w/ the Birdland Big band in NYC...sick, sick playing. also check out M. Buble's tunes. insane players & some of the best arranging i have ever heard. Vinnie, Jeff Hamilton & Rob Perkins (!!!) make it look/sound easy.
if you are new to big band, get yourself prepped for a few demanding styles & genres: things like fast swing (Wind Machine comes to mind), fast sambas, latin styles, Basie styles (Basie Straight Ahead), Buddy Rich intensity & chops (Love for Sale, Ya Gotta Try, etc.) and ballads - these are super important & very, very challenging for me to do these authentically. the rock-solid-good-pocket-feel, hi-hat chick/splash, brush work & cymbal sounds / work is an art form in itself.
the other thing is a good rhythm section. these guys will be your best friend as the 12 horns push & pull the tempos in crazy ways during certain tunes / runs. you will find yourself having to "stick to your guns" w/ tempo on some tunes. particular old-school SWING tunes like "Little Darlin'", "Nice n' Easy, "In the Mood" & "Moonlight Serenade", etc. are the toughest for me as the time feel is super-laid back but *cannot* drag.
i would also record every rehearsal & gig for awhile...you will make amazing progress & have a record of what is going on with stuff you need to change up and fix. it's hard to decipher what is going on sometimes (why does "2" time / feel suck?) when you are in the moment & sight-reading your butt off. recording are also nice to have confidence-wise when a player tells you you are rushing & then you listen to the recording later & find he is dragging all the syncopated figures & can't keep up.
anyhow, with all these challenges...big band is some of the most exciting, richest music you will every play !! when it is ON, it's like you are driving a huge, horn-powered train. i feel very lucky to be able to play big band & jazz for 90% of my gigs around town. took me a while to start getting the gigs (despite the fact that my degree was studio/jazz). the added side bonus is, with most towns...once you are in 1 big band, you are automatically in 4 more as your name gets around the horn players that sub all over & will drop your name to sub as well.