After replying to an emailed question about joining in the bITjAM mix here’s a few ideas to begin with, please add more we’re always looking for innovation in jamming:

When we were all playing beats and acid bass lines, it gets way too messy, so one person does the beats, others add either pads, some lead bits, weird vocals etc. Minimal is better. There’s many occasions when we play nothing while waiting for an idea to pop in to our heads. 
I think the key is sticking to one well known synth and a few very familiar loops or sounds, this saves the dreaded ‘scrolling through sounds while in the mix’ situation.
We tend to agree on a bpm ( we may try midi sync, so midi i/o if you have it) and some ideas around a key (or even the main notes such as C G D) this makes us sound a little more together. 
We have discovered that as long as you can fade ideas into the mix and fade them out the whole things flows better. 
So all in all not rushing into the mix, being minimal, recognising when to fade out, preparing to make strange sounds and enjoying the moment.