Watch the Left Hand Slurs 2 online guitar lesson by Brad Carlton from Essential Techniques
Slurs are the fastest way to develop the left hand fingers. I will show you my personal favorite for developing pull-offs which I label "snaps". Be careful though, 3 to 5 reps are all you'll need per day. I'll also explain why I prefer the term "drop-ons" instead of "hammer-ons." After you develop crisp clean powerful slurs you can then apply dynamics to them thus increasing your expressive skills.