Last weekend I did a dep job on bass guitar for a 16-piece amateur big band. This is not my normal bag. The only regular reading gig I have is with the brass band, which is in treble clef. I did it as a favour to help out the Musical Director and also out of curiousity, to see what big bands are about and whether I could hack it.
The set list was 25 pieces, none of which I'd played before, encompassing Glenn Miller, some jazz standards, soul, show tunes, pop songs from the last century, some oddballs like Birdland, You Can't Stop the Beat, The MD sent me a link to a Google drive with 75 pieces in it, so I decided to wait for the set list which gave me about a month to look at it.
80% of it I was able to sight-read in one take. There were six pieces which were more challenging, mostly fast walking lines in unfamiliar keys or timing issues (Birdland!), so I was lucky to have some time to work these up. Finding YouTube vids of bands playing the same arrangement was very helpful to get the sense of these pieces.
There were no rehearsals. The gig went pretty smoothly, I got lost a couple of times but found my way back. The MD and the band manager were happy with the outcome and have asked me if I would dep for them again if the need arises.
Important points for me:
Stick with the arrangement and don't go off-piste. The arrangement is the arrangement, the MD will point out any exceptions before you start playing. In particular, look first for key-changes and geography (repeats, DS/Coda) before you worry about the notes.
Be confident, and do as much preparation to help you build confidence. For me this includes bringing enough spare equipment so that you can cope with any kind of failure.
Dress code - this is always important and as long as you have black shoes and trousers and a white shirt, bands will provide you with what you need (in this case, polo shirts, but in the brass band world uniform jackets and ties too).
Pay? Dream on. No pay, no expenses, and a 40-minute drive both ways. I got the same as everyone else!