Here is a way of playing a shuffle on the 2nd, 3rd and 4th strings. To hear this style at its best, listen to Robert Junior Lockwood playing guitar on Sonnyboy Williamson recordings.
By now your Blues rhythm playing should be sounding pretty good. If you are a good rhythm guitarist, lots of people will want to play with you, since most guitarists just want to play lead and often neglect developing their rhythm skills. Here is a variation on the previous shuffle, this time in the key of A. The first finger is used to cover each of the first three strings for much of this progression.