Watch the SECTION 9: Improvisation online guitar lesson by Susan Mazer from Hands-On Guitar: The Beginner's Guide
There are a lot of jam tracks on the TrueFire site. Check out the ones that say “A” minor pentatonic and play along. You can also contact people through our blog or chat rooms and try a Skype jam session where someone plays chords and the other person takes the solo. The main thing is to have fun and create.