Watch the Tritones online guitar lesson by Jeff McErlain from Blues Survival Guide: Rhythm Edition
Please watch this segment many times if you are unfamiliar with the way tritones work, if you are familiar, then please watch it again! The motion of the tritone in a blues is essential to both lead and rhythm playing, often as we will see, we can play a blues by just using tritones. It is important to remember that in any dom7 voicing we use it MUST contain the tritone, all the other notes can be changed or done away with but is we leave out the almighty tritone, the chord will loose it's sound. A great thing to practice is finding the tritones all over the neck and use them in a blues form, it's not that difficult once you get the hang of it. More importantly is to get the sound of it!