Try different scales, modes etc. in several positions, back and forth, sequences, arpeggios for about half an hour and then play on and use my imagination. When I go to a place where they are jamming it's a good preparation. Just play the chords during your exercise and go on.
Find a theme , get loose, return to the theme etc.
In the beginning the jam session in the local club starts with a great guitar player. So that you think , oooh I won't play anymore. But after a few times it gets really fine if you dare to play, in the beginning my hands were shaking but after a few times I started to learn and play together with some great guitar players.
