As soon as you've gotten yourself a drink, something to eat, if available, and found a seat, make it a point to get tuned up, check all your gear and be ready to roll. Arriving onstage unprepared and spending the next 10 minutes tuning up and adjusting your cables is a show stopper, and not appreciated. It's disrespectful to the audience and it robs your fellow jammers of precious playing time. Don't rely on the jam hosts or other musicians to lend you cords or instruments.
Please remember that you are a band member.
On nearly every jam set, you'll find that the band is led by an experienced player/singer who will choose the songs and hand out the solos. They'll always try to make sure that every other player who wants to play a solo gets at least one opportunity per number. When that opportunity comes your way, go for it!
Then, no matter how impressive your chops might be, revert to being a member of the rhythm section while others play. "Sit in the pocket" and give your fellow jammers room to breathe. Squash that urge to fill every spare moment with a note or riff. Don't splurge all over someone else's solo or let your rhythm-playing drown out their lead.Above all, keep eye contact with your fellow players for signals, stops and tempo cues.
It is imperative that you give vocalists room to sing. Playing over a vocalist, in any capacity other than quiet rhythm, denotes a "stage hog" or someone who is unable to play with a group. Please be respectful of your vocalists. Turn down and back off when they are singing. Anyone who plays over vocalists, or treats other jammers who are soloing without respect, will be reminded of this.