Watch the Big Bend Blues online guitar lesson by Jeff McErlain from Blues Guitar Survival Guide - Lead
Vibrato plays a huge role in this as well, bending and adding controlled vibrato takes some real work and focus. I know I have covered this before but it must be practiced with intent, almost meditate on the notes and vibrato as you do it. Make mental notes as to how much you are pushing or pulling the string, concentrate on the note being in tune. Record yourself and listen back critically. It's this approach that really tightens up your blues playing. We should never leave these things to chance!