Your role in a blues jam is to play the chord tones of the chord progression (the 12 bar blues progression is fairly cut and dried) and stay out of the way of the solo instrument. If there are drums, lock in on the kick drum, if there are no drums you are the beat master - keep the beat with a basic bass line.
The 12 bar blues progression:
- Four bars of the I chord, or some will have one bar of I chord, one bar of the IV then two bars of the I chord, then
- Two bars of the IV chord, then
- Two bars of the I chord, then
- One bar of the V chord
- One bar of the IV chord
- One bar of the I chord
- One bar of the V chord to loop back and start over. If ending the song let the last two bars end with the I chord.
Here is a video lesson using only roots. http://www.youtube.com/watch?v=Gqhxxqhvw_4
Here is a backing track http://www.youtube.com/watch?v=CqtljIOCQpM
- see what you can do with this one, it's going to follow the 12 bar progression listed above.
I think backing tracks will help you more than specific songs. In a jamming session they will call out the name of a song and give you the key. No guarantee that you have even heard the song before, but, you are expected to lay down a bass line. Knowing the key and then pull up your basic 12 bar blues progression and winging it till you get a feel for the song is what happens in most jamming sessions. Listen for the chord changes, when you can anticipate the changes, and know what will come next - that's half the battle.
See what you can do with these backing tracks. http://www.youtube.com/watch?v=6RTgTIhjhUM http://www.youtube.com/watch?v=dskqGNgHxJA http://www.youtube.com/watch?v=dTrxD0s6OsI
The last four bars are a little different on this one. Be aware the 12 bar progression is not cast in stone. The first four bars can take the "quick change" of adding the IV in the second bar and then the last four bars can end with the dominant chord to make the loop back or just end with the last two bars being the tonic I chord. A quick question to the rhythm guitar; "Is it a quick change in the first four bars" and then take for granted it will end with the dominant chord and loop back.