Generally the way it happens around here:
There's a house band that does the first set. Bassists don't tend to bring their own instruments because of the space issue, so whatever you're playing will be the house bass. (although bass guitarists will likely bring their instrument). If you are using guitar, then you're not gonna get pianists to show up. If you're the master of ceremonies for the evening, IT'S YOUR JOB to make everything go smoothly. If it's a small session and you know everybody there, then you can play it kind of loose and just call cats up to play. DON'T LET EVERYONE PLAY ON EVERY TUNE. If it's a large session and there are folks you DON'T know there, HAVE A SIGN UP SHEET. You need to know WHAT INSTRUMENT and WHAT TUNE they want to play AND you don't have 6 tenor players blowing on the same tune. You're gonna have to keep an eye on the time and the number of folks waiting to play; if there are only a few folks on different instruments then you can bring up more people to play on a single tune and they can play more tunes, but if it's a lot of people and mostly only one or two different instruments, folks may not have a chance to play more than one or two tunes.
BE KIND TO YOUR RHYTHM SECTION. If there aren't a lot of section players showing up (bassists sometimes have it particularly hard), don't keep your drummer or chordal instrument on stage all night. Give breaks.
KEEP THE HOUSE BAND CLOSE - if things start to degenerate, you can re establish control by bring the house band back up to perform an obscure tune that you have arranged out the wazoo to keep Erstwhile Ingenues in their seats.
AND FOR MITHRA'S SAKE - DON'T LET A TUNE GO ON FOR 20 MINUTES. Don't nobody want to hear that.
And just a caveat - if James Carter shows up , his first chorus will be everything you just played verbatim, his second chorus will be all of that double timed and, when he gets bored with that, he'll show you how the tenor is SUPPOSED to sound....