Watch the A minor Blues: 1st Chorus online guitar lesson by Robben Ford from Riff Revolution
This particular chord progression is a 12-bar blues, and it opens with a series of the last 4 chords of the progression. The first chord is a flat VI chord, so it's an F7. We're in the key of A, so it goes F7, E7, A minor.
What I'm doing here is playing straight up A minor pentatonic, with these notes working against the flat VI chord. However, you can't play in E - you can play all the other notes in the A minor pentatonic against the F7 except the E. The choice of pentatonic notes against the flat VI chord is essential. You can't just run rampant.