I control the PG mainly. I sag off the opposing PG, daring him to take a jumper (they usually don't). If they run one of the plays designed to free up the SG or SF on the wing for the jumper, I attempt to do a fly-by (run at him to contest the shot). I play the passing angles, try to go over picks, generally rotate whenever I see someone open. I also sprint the C and SF back after made baskets (they usually lag), and then take control of PG. After misses, I focus on the ball and attempt to slow the ballhandler down before he reaches the top of the key.
I'm now setting my defensive settings to:
SF, SG play tight on-ball
PG, PF, C sag off on-ball
all sag off off-ball (if a guy starts killing me w. jumpers I play him tight off-ball)
all doubles never (unless a guy starts murdering me)
Just try to get a hand in the shooters face, run to rebound, play smart positionally and rotate.
I'm not great, but I do o.k.