Watch the V To The B online guitar lesson by Jeff McErlain from Solo Factory: Chicago Blues
I particularly like this lick as it really outlines the V7-IV7-I7 turnaround by simply sounding chord tones. I start off on the V7 chord (B7) by playing the 3rd of the chord which is D#. This is an important note as D# is not a particularly good sounding note on the E7 and A7 chords, but a great note on the B7. By using this note be really bring out the sound of the V7 chord. When I get to the A7chord I simply play the C# and G which are the 3rd and b7. So by using very few notes I outline the sound of the changes. Playing over changes can be difficult for sure, but the blues is a great place to start.