talk to and listen to each other.
this, more than anything else, has kept my jam sessions fun and satisfying.
keep the dialogue going on both a verbal and musical level. tell your partners you plan to drop in a new top rhythm in 16 bars, or pull out your kick, or fade in a pad. count it in for them (“in 3… in 2…”) so they can plan to react appropriately when you do.
maintain eye contact. look around frequently for a vibe check. ask them if they think one sound or another of yours is working. if they think it isn’t, tell them you’ll replace it in X bars, or ask if they’ve got something they can try to replace it with. listen and tell them your impressions.
leave space for them to talk. it’s easy to fill up lots of sonic space with even one electronic instrument. if three people have three instruments each, you can quickly create a traffic jam rather than a jam session.
for long stretches, your contribution might be a single subtle monophonic line, or an occasional clap, or nothing at all. that’s ok. you’re not giving a speech, you’re having a conversation. sit out entirely for a few minutes and listen.
pump them up when you like something they do. if it inspires you to add something complementary, tell them you’ve got something to go with it that you’ll drop in 3… in 2…
this kind of approach helps you get to know each other musically and also perform with your gear in real time. bonus: i’ve noticed that audiences really respond well when they see electronic musicians communicating onstage … they see something happening they can relate to, so no one suspects you’re just up there checking your email. win-win for everybody.