When you set a screen on a defender you must plant your feet and remain stationary, keeping your arms close to your torso. If you hold, lean or move into the defender to cause contact you will be charged with an illegal screen foul, and the ball will be turned over to the opposing team.
You can’t cut into the defender’s path and hit him with a screen while he’s on the move. If you step into the defender while he’s moving to cover his man, it’s a foul.
During Thursday’s matchup against the Blazers, Carmelo Anthony got his fifth foul because he knocked into his teammate’s defender rather than planting himself firmly alongside him when he attempted to set an on-ball screen.
[nba-video vid=channels/tnt_overtime/2010/11/23/czar_carmelo_foul.nba]
The Official Website/Blog of Mike Fratello 
[…] at his blog, one of the things that Mike Fratello talks about is how nobody really sets good screens anymore: In order to set an effective screen, you must establish the […]