Focus on the proper footwork first, that is the biggest secret to good fielding. (It also is the secret to accurate throws!).
In the Diamond Edge podcast, Episode 10 gave advice to players on how to prepare for tryouts. This is good for coaches to listen to also. Click here to listen.
Also, there is a good entry in the Coaches’ Journal on the St. Louis Diamond website titled “What Smart Coaches Look For”. This is a summary of some research that I did last year with high school baseball coaches. Click here for the journal entry.