A word or two about volume. Don't worry: we'll let you know if you're not loud enough - and we'll let you know if you're too loud. Don't be offended if you're asked to turn down. You are on a small stage, and can't hear how loud it is in your audience. It's up to you to make sure the vocals will be heard above your instrument. Keep it sensible. Remember, The Blues is a subtle genre, filled with dynamic highs and lows. Louder is not better. If it doesn't sound good quiet - it won't sound any better at ear-bleeding levels. If you play full bore, you'll have no dynamics to play with - and, very quickly, no audience to play to.
What we're accomplishing is not Karaoke. A blues jam is a place for seasoned musicians and newcomers to gather. Please don't jump on stage if you're drunk and insist on singing. We're not adverse to folks drinking. We just want an honest, professional jam. So if you want to party, wait until after your turn and buy one for the host band too!
Believe it or not, I have heard players say they should be paid for their part in a blues jam. If you are booked so solid that you don't want to share your music and join in the comradery with other musicians, you don't belong at a jam. It's a place to practice your craft, appear on stage, let people know you're in town and a viable player.