To start, I drew the basic shape of a guitar with the paintbrush tool and one of the brushes from the brushes palette (though I can’t remember which brush).
Then, I selected the drawing with a selection tool and went into the brushes palette again, this time clicking all the various choices. These from the “Decorative Banners and Seals” were the most interesting results.
Starburst 2:
Starburst 3:
Starburst 6:
Uncharted Planet 