Watch the Forward Roll online guitar lesson by Ben Wright from Bluegrass Banjo for Guitar Players
Now add the G, C and D7 chord progressions to the exercise. Once you learn these and other chords on the banjo, you'll be able to essentially translate what a guitar player is doing in a jam situation. Knowing guitar chords puts you at a major advantage in playing situations. If you get lost, you can always sneak a peek at the the guitar players left hand.