Practice trilling with your ring and pinky fingers (especially that pinky). I find that in my playing I use my index finger and pinky finger in almost everything I play. The ring and middle fingers only get about half the action that my index and pinky get.

Trilling - Only pick the first note. The rest are hammer-ons and pull-offs. Try to keep it up for 30 seconds at first, then a minute, then two, and so forth. Great thing to do while talking on the phone or watching tv.

index and pinky
|5-8-5-8-5-8-5-8-5-8-5-8-5-8-5-8-5-8-5-8-|

index and ring
|5-7-5-7-5-7-5-7-5-7-5-7-5-7-5-7-5-7-5-7-|

index and middle
|5-6-5-6-5-6-5-6-5-6-5-6-5-6-5-6-5-6-5-6-|

middle and ring (this one is hard to do at first)
|6-7-6-7-6-7-6-7-6-7-6-7-6-7-6-7-6-7-6-7-|

ring and pinky (this one's hard too)
|7-8-7-8-7-8-7-8-7-8-7-8-7-8-7-8-7-8-7-8-|