That it either moves fast, or that everyone is involved at the same time. You don't want anyone standing around for long periods of time, or they'll lose focus and good luck trying to get it back.

Make the drills fun.

First couple of practices just work with basic foot work skills and moving the ball and shooting, but always keep it moving. After the basics have been covered for a couple of practices, start to involve passing drills and stopping the ball drills with another teammate. I would only stay with groups of 2 so that all the kids are touching the ball.

Someone fun that I use to do to end practice, would be either some kind of relay race, and I would get the parents involved with this as well either cheering them on or somehow would involve the mom's. OR, I would have a shooting contest.