It's a BLUES JAM, folks - not an open-mic night. What this means simply is that if you are a budding singer-songwriter, and you're looking for a platform to showcase your latest collection of power ballads, you've come to the wrong place. We play the blues.
Expect to play with other players. There is a full back line, (check to be sure there's a keyboard) and you'll likely be playing and/or singing with a guitar player, drummer, and bassist. There may or may not be horns in the mix.
Lots of jammers say they "want to let the house band play before they arrive." There is no set time for the house band to play, and often get jammers are invited to play with the house band initially, so, you snooze you loose.
Always bring your own instrument, cable(s) and tuner. In an emergency, a fellow player might consider lending you their gear, but you should never just turn up and expect to borrow equipment. Drummers can relax, though. Keyboard players check ahead.