I don't really know how to play the blues well. I know a couple of chords, a scale, and how to fake it. This video will show you the basic idea of what I do. Although I've called this a beginner blues piano lesson, it's really aimed at those who know their chords reasonably well and can follow a fast bluesy run on video. The basic progression I use contains only three chords - C7, F7 and G7. These dominant 7th chords based on the I, IV and V are typical of blues. I also use the C blues scale to form riffs and runs.
C Blues scale = C Eb F F# G Bb C
However, I only adhere loosely to this scale, as I sometimes include a D or B as passing notes too. In other words, I use the C blues scale to create that bluesy feel, but glean from the C major scale for variation. If you watch closely, you'll notice that I'm using the same riffs and chord structures over and over. I'll change the inversion of some of these chords, alter the length of the riffs, but really, it's the same basic stuff played repeatedly and disguised as something different. Hope you learn something from this beginner blues piano lesson :)