As described in more detail in Progressive Blues Harmonica, a "Third Position" blues harmonica lick or solo is one in which the key of the harmonica is one whole step beneath the key of the song. Thus a key of C harmonica is used to produce a Third Position song or lick in the key of D.
The following Third Position Blues Solo may be played either using single notes or not. Practice playing Lick 7a, below, before attempting the entire solo.
Now play the entire solo, using a three note chord for each beat.
Once you have mastered the Simplest Third Position Blues Solo using one chord for each beat, you may play the solo utilizing single notes. This can be achieved simply by replacing each 456i chord with the single note 4i, each 567e chord with the single note 6e, and each 567i chord with the single note 6i. Practicing Licks 7b through 7e will help you to accomplish this.