Here is another classic rhythm guitar part in the style of Chicago Blues great Magic Sam. The tonality here alternates between minor and dominant seventh sounds.
This one will probably sound familiar to you. It has been used by everyone from Muddy Waters to the Blues Brothers. Notice the use of space which leaves room for the singer, or for call and response with the lead instrument – often a harmonica or slide guitar.
Once you have control of the basic riff, try making up some variations.