Probably more important for Blues than the major bar chords are the root 6 and root 5 7th bar chords. Shown below are shapes for G7 as a root 6 chord and C7 as a root 5 chord. Like major bar chords they can be moved up and down the fretboard to any key.
Practic changing between these two shapes, then try this 12 bar Blues which makes use of both, along with a root 5 D7 chord at the 5th position. This progression contains a common blues variation, moving to chord IV (C7) in the second bar. This is often referred to as a Quick IV. Once you are comfortable with this example, try reversing the order of the shapes, i.e. beging with G7 as a root 5 chord and use root 6 chords for C7 and D7.