We got a guy around here who looks, acts, and talks like a really great blues harp player. He's got the modded green bullet, ancient tweed Champ, a custom matching distressed tweed harp case, and knows all the right lingo and phrases. Only problem is, as one of the better blues guitarists around here said about him, "he really wants to be a great blues harp player, but he's just too white to pull it off." First thing is to relax, don't get hung up on the genre and serve the music
Don't concern yourself with extrainous details. Load up your playlist with blues tunes, preferably their set list, and cram that 24/7 and set aside as much time as possible to translate what you've heard to music. Concentrate on being on time for changes. Stick to the basics for a minute until they come without thinking.
Once you get the job, work hard on your on stage communication skills and become an observer of the left hand of your guitar player. If they are a serious blues band they will follow the advice Lightning Hopkins gave Dusty Hill when Hill complained about having trouble following Lightning through the chord changes "Lightnin change when Lightnin wanna change". Having been lucky enough to have played with the late great Willie King, i can assure you this is sound advice. Concentrate on your fellow band member's "tells", that and prearranged cues will make or break a blues band. You can be the most technically competent band on the planet but if your product is nothing more than pre measured portions of notes and words, you are just another sterile blues-like product and your audience will feel it and will cut you lose to chat and prattle rather than bear witness to y'all testifying.
My first job with a blues band was a call from a drummer i'd been working with for a while. He called from a club and said their bass player bailed at the last minute, could i come down and fill in. I told him i'd never played much blues and he said no problem, just follow him and watch the guitar players left hand.
I know you will pull this off no problem, but blues is much more fun if you can just relax and flow with the music rather than try to force things.