Watch the Tritones online guitar lesson by Jeff McErlain from Blues Guitar Survival Guide - Lead

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!