Well, he does appear to do what you're asking for. Hope that it will work, you can only try.

Consider that improvising will mean you have to develop your ear. The previous advice to learn to find the melody is sound. Most guys will do a solo first staying close to the melody, then departing to come back. That said, there are no hard rules other than perhaps the most basic of rules which is;

If it sounds good, it is good!

I learned to improvise when I was learning the accordion. it's different there, but in many ways the same. I had learned the scales, chords, chord inversions, intervals and so on.

Then my teacher had me find a rythem and then slowly...build a melody to that rhythm, and play it till you got sick of it. Then get another rhythm and do it again. and again....and then when you need that stuff it will be there. Worked for the accordion, but I wouldn't say that it exactly translates to the Mandolin.

You're going to have to learn to hear the scales and so on and you'll get that by learning to find the melody. Try that first.

It helps if you play guitar and put down some rhythm for a song on tape and they try to play to it, improvising. That should get you started.

Let us know how you're doing.

-- Jim Polaski "The measure of a man is what he will do knowing he will get nothing in return."