When playing this type of shuffle, it is common to damp the strings slightly with the right hand. This results in a tighter, more chunky sound. Rest the heel of the hand on the strings at the bridge and then pick the strings you want to sound. It may take a bit of practice to get the desired sound, it all depends on the exact position of the right hand and amount of presrue used on the strings. Here is an example.
Now try applying the right hand damping technique to this 12 bar Blues.
Here are some variations on the basic shuffle pattern. Learn each one then apply it to the 12 bar progression. This next one requires the use of the fourth at the fifth fret.
Like many Blues rhythm guitar parts, this idea originally came from a Boogie piano pattern.
Here is another variation. Try making up some of your own.