Since you guys all have so much technical information on how to improvise, let me write about the attitude.

When you are improvising, there is NO SUCH THING AS A MISTAKE!!! The gol-durn things just don't exist for as long as you are improvising. What there is, is an interplay between dissonance and resonance... (Otherwise known as "clangers" and "harmony notes".)

Any so-called "clanger" adds tension. Some notes add more tension than you would like, but that happens. Any "harmony note" is a release of tension...

This happens in life, too. You go along, minding your own business, and sometimes you're happy (harmony note), and sometimes you're not (not-quite good note), and sometimes you get in an argument (clanger), but then maybe you resolve it (harmony note) until the next time (not-so harmony note), or maybe you agree to disagree (not-so-harmony note).

There is a philosophy I use when I improvise, that everything is in the right moment... it's almost religious. (But don't tell anybody... shhhh!)

Improvisiong is just creating a flow of tension and release over the duration of the song. That's all.

After that, you can learn the scales, and add them into the philosophy, so that you can craft the amounts of tension and release that you want to put into it. But if you have that philosophy, then you will love improvising, and it will be a lot easier for you.

(If anybody can understand what I'm saying?)