As mentioned previously there are many variations of the 12 Bar Blues progression. The first of these variations inserts the V chord in the 12th bar. Try the following example in the key of A.
Rhythm Pattern
To play the B7 chord, use all four fingers of your left hand as shown in the diagram. Strum only five strings.
Another common variation on the 12 Bar Blues progression is to substitute the major chord with a seventh chord. This helps provide a more "bluesy" sound to the progression.
The following example makes use of the seventh chord including the B seventh chord, used in bars 9 and 12. This time the key chosen is E.
Rhythm Pattern