Exercise 1 
Here is a blues box in C
Try using these partial seventh chords shown below as "stab" chords. Quite often when playing soul and jazz using the 12 bar blues form, guitarists will be expected to use "stab" chords to add to the rhythmic drive. You can try to play these on the backbeat (play the chord on the snare) or just as a "down-stroke" on each of the four beats in a bar. Note the fingering and the fact that the second finger stays on the same string. The fingering is important because it allows easy movement between the chords and fast tempos can be tackled with ease:
Exercise 2 
Here is a blues box in Dm
You can play a blues using only minor seventh chords. In most cases where you form a half-barre the first finger will be used but for the Gm7 and Am7 below you can use the third finger. The choice is yours though I think you'll find in this instance using the third finger is more comfortable.
In this variation you will be using a single chord shape to play the twelve bar blues. Fingering has been given for the Dm7.
Exercise 3 
Here is a blues exercise in A using sevenths.
These sorts of blues riffs were taken by other genres and moulded into something entirely new. The exercise above can be easily approached as a "surf" riff with distortion, reverb and fast picking in a similar style to the 1950s track "Wipeout" by The Sufaris. Rock and soul riffs can also be derived from the blues. For a soul feel, try jumping from the first note to the seventh when starting this riff rather than following the linear pattern. The seventh is easily recognised as the highest note in each bar of standard notation.
Exercise 4 
Here is a typical blues rhythm.