The arms should be folded at the elbow and the fore-arms should be used to protect the body's vital parts but not used to extend outward to make contact with a defender which will result in an offensive foul call. On any screen where the screener is in the field of view of the cutter's defender, the screener may and should make body to body contact when possible without fouling. However, on back screens or where the screener is out of the visual field of the cutter's defender, you must allow one step for the defender to change directions or any contact will result in an offensive foul call on the screener. The next step is to teach your players how to use screens. First by teaching the cutter to run their defender into the screen by starting off with a V-cut toward the basket.
Some coaches teach walking the defender in, other's two hard sprint steps.
The bottom line here is use the technique which puts the defender between the cutter and basket which forces the defender to trail a cutter off a screen. If the defender gets between the screener and the cutter, the cutter should look for the back door cut. The cutter should run off the screening player should to shoulder to prevent any chance the defender may slash through and break up the screening action. On screens occurring away from the ball be sure to teach your cutter to get their hands up as they pass the screener so they are immediately prepared to catch and shoot or pass the ball off the screen. Finally, the most critical element of all screens is the timing.