In blues ‘dominant’ 7 chords (A7 or D7 for example) are more common than basic major, minor and sus chords. The A7, D7 and E9 shapes shown here are all you need for a 12-bar blues improv in the key of ...

To do this, tune into open G by dropping the sixth, fifth and first strings down a tone, then drop the second string down a semitone to a Bb – that’s the all-important minor 3rd in the key of G.