Soloing

I am an improvisational blues/rock guitar soloist, rarely playing the same solo verbatim twice (unless it's very well known and/or integral to the song like "All Right Now").

I tend to think of improvising with a musical instrument as being akin to improvising speech. For example, if you are familiar with the subject at hand and the context in which you're speaking, you don't need to write out everything ahead of time, just speak. Let the words flow naturally as the ideas come into your head.

The other thing - really just an elaboration of the above - I would recommend to your friend about improv soloing is this: learn all the theory you'll need - for jazz, that's a lot. The greater your "vocabulary", the more "literate" you are. Work up your chops so you can manipulate the keys/strings smoothly, quickly, and accurately. Then, when it comes time to solo, be prepared to forget it all. Don't think about it; let yourself fall into the music like falling into a pool of water. Try to "get out of the way" of the music inside you and let it flow through you as if you were merely a conduit. Trust all that training and practice to serve you well, just as you would if you were driving a car. Or better still, making love.

Best wishes to you and your friend!

Have him do a solo with two or three notes only.If his attitude is that this is stupid or he can't do it then This is a major part of his problem.If you only allow him two or three notes he will be forced to seek out the "feel" and rhythm, The essence of a solo. Adding notes is the easy part. You have to 'not try' in a way.Forget about the technical.Forget who your trying to impress.Clear the path to make that disconnected connection between baseline and solo.