A great way to make your ball screens more effective, and to keep the other teams big man from aggressively extending out on ball screens, is to have your ball screen man slip the ball screen. Once the screener feels his man on his outside hip he/she should slip right to the basket for a layup or dunk.
Once this happens a couple of times the defensive big man wont cheat out as much on the ball screen, and this will open it up for the ball handler to turn the corner and make a play. Keep the defense honest and get easy buckets by learning how to slip a ball screen. Basketball drills like this are all about working on the details of the move, really pay attention to the video and watch the angle of the screen, the cut, etc.