i've only ever really collaborated with people i already knew to some extent, but generally whenever i've reached out to those people, they've been interested and/or excited to do the thing!
Elemental Fusion is 100% collaborations with instrumentalist friends, and i very much want to do another project in that vein, perhaps in deeper collaboration with the peoples - in most of the cases on Elemental Fusion the instrumentalist part came first, and i went from there... but it'd be fun to do some planning and songwriting too.
in terms of "what works", i think you wanna be looking for the same stuff as you would in a song-writing collab, which is just synergy more than anything, a reason to be collaborating where both of you can have fun. i haven't really had a bad experience doing this ever, so i'm not sure what else to avoid! it's bound to be a lot different commissioning strangers. maybe the first place i'd think of looking would be Bluesky? or word of mouth from asking friends.