A useful thing to learn is about chord construction and voicings. It can be very useful in rock and blues to know how to voice chords differently so that all your songs don't have the same kind of sound. It is also very useful to know that you can play a chord at any point on the neck, so that if you play a chord in a certain position you only have to move a few fingers to get to the next chord. Chord inversions come into play a lot in that instance, where you play a chord but make the third, fifth, or even seventh the bass note. This means you can change chords but keep the same note on the bass which can be useful. This is my idea of what would be useful, if you want me to actually explain some of the theory I would be happy to.