one good way is to practice some simple scales, like the G major scale and make sure you "pluck" the string with your right hand in coordination to freting the note with your left hand.
don't try to practice speed, just try to get every note to ring nicely.
this exercise will help you control your digits, as well as teach you some scales on the guitar.

(the link is from Dansm's guitar site)
http://scenicnewengland.net/guitar/

good luck
adam