As well as using 7th chords with the right hand, it sounds very effective to add the b7 degree of each chord to the left hand shuffle pattern. Here is an example using the shuffle pattern for a C7 chord.
Once you are comfortable with the pattern, practice it on the last four bars of the 12 bar Blues progression. This gives you all three chords for whatever key you are in. In this case it is the key of C, so the chords will be C7, F7 and G7.