Watch the Magic IV online guitar lesson by Jeff McErlain from Solo Factory: Chicago Blues
Magic IV is a great example of how simply we can play on a chord and be extremely effective. The lick basically outlines an A7 chord which is functioning as the IV chord in an E blues. The trick he is the bend on the b7 or G note of the scale. A7 is spelled AC#EG but we want to bend the G a little bit to give it a little mojo. That note really wants to pull us up to the root note A, but by never getting there it adds some great tension. Experiment with tweaking the b7 of any dominant 7th chord.