Watch the The Turnaround online guitar lesson by Jeff McErlain from Focus On: British Blues
I think the first time I was aware of a lick nailing the sound of the V7 in a blues was the great solo from Cream's version of Crossroads. In fact it was a real eye-opener for me and once I was aware of it, I began to hear it everywhere. In this case I am playing an A blues, simply hitting the root of the V chord—E in this case—on the second half of the last bar of the blues. It's that simple and that difficult! What makes it difficult is that we're required to know where we are in the blues form to hit that note at the right time. It's not too difficult but does require some practice. The best way to do this it to make sure you hit that note every time you play through the blues. By doing this you can really nail where that note is and where the change is.