This is how my band and I practice/write.

We have 2 sessions a week which are typical practice rehearsal sorta stuff. Then throughout the week (The 3 of us live together), we'll get together for an improv jam session. Sometimes it's just for 45 minutes or whatever before work or what have you. But we record all of these, and make a note of interesting/cool things we came up with. Everynow and then our practice sessions are just listening to previous recordings, seeing if there's anything we'd forgotten about or want to try, making lists of things to work on.

A lot of really cool stuff comes from that, and it's also really helped us play together better as well. The synergy that comes from it is awesome, and it's also a good stress reliever. Just jamming, mistakes don't matter, just play through them or switch to something else. We'll play for like 30 or 45 minutes straight sometimes just playing with a particular groove or progression, other times we're all over the place, switching from jazz to metal to more country/bluegrassy stuff to just some insanity that even we can't make sense of lol.