I didn't want to participate to bc for different matters anymore, but anyway: this topic is too good to leave it behind.
after 33 years of being in the "biz" mostly on the creative and not the reproductive side, all I can say is: join [b]every [/b]"original" jam you can find. there is no better way to find your individual voice on your instrument, than jamming with great musicians (even not so great is good enough in the beginning - always try to play with better musos than you are).
nowadays a "jamsession" seems to be a simple open mike with mostly poorly performed covers. for sure good enough for most of the people in the audience for being easily and simply entertained...
but - when I started in the early 80s, every band that just had found each other started with a jamsession. one guy had a beat or a riff and off it goes. If you were lucky, it was the sketch of a new song the way as others here on the had mentioned. you went on and this was a way how a live set was completed in the beginning: [b]organic[/b]....It never was about theory, rules and stuff. it was just about emotions and about [b]LISTENING TO EACH OTHER[/b] while we were playing.
back to 2015: times have changed. theory, scales, chords and composing systems are tought in all these "music" schools around your place or even online, most of the newly "released" musos know their theory, but...
...what they mostly lack is [b]LISTENING[/b] and [b]CONVERTING[/b]. No scale or chord structure will help you with improvising spontaneously, if you don't connect to what you listen to. the most important thing of being a muscian is mostly underestimated nowadays: [b]being able to listen[/b] to what is surrounding you (what good musos should do ). music is the most rewarding way (for me the most direct, the most beautiful, the most international and intercultural way to communicate and directly being able to see the heart of your "opponents" and the only way to interagitate with every unknown human being in a peaceful way. use it, listen, learn and teach your pupils to be able to communicate on their instrument, if you want to make this world a better place.
jamming with great musicians for me is the highest and most rewarding way of living expressional music that exists. so grap every chance you get, spread the thought and keep the ball in play!
cheers from germany!