The 12 bar blues progression is something you have to understand and familiarize if you ever want to become a master of the blues. The blues progression is based on the 1-4-5 chords of a key.
This blues progression is really simple. Basically, we are doing an Am7 going to a Dm7 to the Em7. These chords make up your 1-4-5 pattern.
The riff is simply a slide from the 5th fret right on to the 7th fret of the 5th string followed by going through the pentatonic scale and stopping at the A note which is on the 4th fret of the 4th string.
To put this together into a blues progression, start by playing the Am7 chord. Then, execute the riff discussed above. Next, play the Dm7 chord and play the riff pattern again. But this time, start at the 4th string. After that, play the Em7 chord and execute the Am7 riff again.
Practice this blues progression and make your own variation. You can even try playing the riffs along with the passing notes between it.
12 Bar Blues Progression and Riff
12 bar blues progression and riff on youtube.