Points to Remember:
• The blues originated with American slaves, but it's influence has touched every form of modern music. "If a song ain't got a bit of the blues in it, it ain't good for much."
• Blues often uses "dominant seven" chords. These chords are made with a Root (1), 3, 5 and b7 (flat 7). Dominant seven chords are usually just called "seven" or "seventh" chords. Dominant 7 chords have a "bluesy" or "funky" sound.
• "Major 7" chords have a "pretty" sound, and contain the basic 3-note triad (1-3-5), plus a major 7 (the seventh note of a major scale).
• A 12-bar blues in A would be:
4 bars A;
2 bars D; 2 bars A
1 bar E; 1 bar D; 1 bar A; 1 bar E.
So obviously, it's the last 4 bars that are the trickiest, since you have to change chords every bar.
• After you run through it a few times it's a good idea to practice it with a metronome or drum track. (Google 'metronome' to find free online versions.)