I liked Eddie's Ten Commandments For Old-Time Music Sessions above and feel that they are appropriate for all music sessions. However, the Commandments should not stop at ten; how about:-

XI. Thou shalt never try to dominate the session by always being the one to start off tunes, even if it is clear that thou art the best musician there.

XII. Thou shalt encourage the quieter, apparently timid musicians to take their turn in starting tunes, particularly young women, for shyness and apparent diffidence does not mean that they are not excellent musicians with a good repertoire.