Watch the Trill Drill online guitar lesson by Gary Hoey from Blues Rock Reactor
Now let's take a minute to talk about the left hand and a couple of things you can do to strengthen it, which I call the "Trill Drill". What's a trill? It's when you hammer-on and pull-off in quick succession. It's good to start out doing this with a metronome (but you can go without too), but start hammering-on by playing sixteenth notes at the 8th fret from the 5th fret of the E string with your pinky, then move a fret down using your third finger, and then your second. Try to each one of these for 30 seconds, starting off at a slower tempo and moving up to faster trills. Then, try mixing up the combinations of fingers you use to stretch the exercise further. You'll start to feel the burn in your hand and wrist, so don't overdo this one too much and strain yourself!