Coach,
Not going to share any "earth shattering" information here, but thought I'd mention the things I have done over the years to promote sound outfield play.
I'm assuming you are looking for drills for high schoolers? If so, here goes.
1. Make OFers feel like they are important! They need to know that an error by them will cost two bases, not one like an IFer. This will happen if they are made to run bases all practice. Expect alot out of your OFers, but only if you invest alot in their practice time.
2. They need to field ground balls like everyone else. Have them take a spot in the IF and let them do the IF drills with the rest of the team.
3. Once they are in the OF, drill the things that happen all the time. Not the things that rarely happen (ie. fence drill, do or die, etc...). Not saying you shouldn't practice fence communication, but a couple of minutes each day is plenty.
4. Teach them to field groundballs based on the situation and playing surface. With no one on, or with poor OF conditions, getting in front of the ball, even dropping to a knee, is good practice. With runners on base, they need to field the ball more like an IFer. They need to learn the proper technique for crow hopping (I like to overexagerate the crow hop at all times).
Kids calling me...I'll be back.