Another effective method of playing a shuffle is to rock backwards and forwards between an E chord shape and an A chord shape. Here is an exercise to help you gain control of this technique.
Here is the technique applied to a 12 Bar Blues shuffle.
This example uses a variation on the rocking technique. Take care with the top note of each of the chords here. Sometimes the highest note is on the first string, other times it is on the second string. This one also contains a chromatic run between chords I and IV.