Another way to be very productive is to invite other musicians and have a go and making music. Depending on the configuration you could get all kinds of unexpected results.
Usually I think the best is if the musicians are independent and could play anything at anytime. Being a good musician helps, but it’s the attitude of jumping out to the unknown and play is that counts. It’s hard to get anything going if someone is constantly asking for directions. Same with arrangements, in the case of songwriting the arrangements are of secondary nature, but the musicians should be strong enough to make their own arrangements as part of the sessions to create music.
Then all you need is to record all the sessions, whatever happens, just record it. Have an open mind, not rules such as: “we should do ten songs or otherwise we can’t leave the room.”
I must stress again, this is like constellations, some configurations work extremely well, others barely, some not at all, you need to test out various configurations.
PS: That image is of an MusicMan guitar amp I saw last Saturday. I have seldom seen them here in USA. I used to have one in the early eighties, fun amps, good for rough rock blues sound.
PSS: If you are in the Bay Area (San Francisco) and need someone to do such sessions, just contact me, if I have time I show up. This is of course with AAAFNRAA in mind: “Anything, any time, anywhere, for no reason at all.” (Famous Frank Zappa motto.)