Listen to Willy’s Blues for an example of this type of blues progression.

The blues is typically 12 measures of 4/4 time (4 beats per measure) or in other
words, a 12 bar blues.  These 12 bars repeat over and over for
the duration of the song.  The most basic form of the blues
has 3 chords that follow a I-IV-V progression.

In the key of E, the chords would therefore be E, A and B.   In
the following diagram you can see that you would play E for 4 bars, A
for 2 bars, E for 2 bars, B for 1 bar, A for 1 bar, then E for 2 bars.
 Then the cycle repeats.

We’ll just stick to the basic major chords for now.  Check out the mp3 sample as well.

 This progression is a shuffle feel (the 2nd eighth note of
each beat is delayed giving it a swing feel).  There is piano,
bass and drums accompaniment for 2 choruses (2 times through the 12 bar
progression).  For now we’ll stick to basic major chords.
 You’ll notice I just play 2 notes - the root and 5th of the
chords.

Listen
to mp3

Variations to Blues progressions

Once you get a handle on the previous progression we can start to modify it
to make it more interesting and to show some typical modifications that
are made by blues musicians.  If you notice in the last
progression that the first four bars contain just the E chord.
 We can spice this up a bit by adding the IV chord in measure
2.  In bar 12 (the last bar) we also add the B chord which is
the V (the dominant chord which has a strong tendency to resolve to the
I chord - that is back to the E chord).  

The recording plays through 2 choruses (2 times through the 12 bar
progression).
Listen to mp3