When playing zone coverage your players must know their area of responsibility, where the help is coming from, if any, field position, strength of offensive formation, etc. Pass drops should always be controlled by the secondary personnel, so they can read patterns and be ready to break and drive on the ball. Secondly, when the quarterback sets up and is ready to throw, the secondary player should set and be ready to react. Always be under control, so that you can move to the ball when it is thrown. Defender should try and work to keep his shoulders square when reading the quarterback's eyes, shoulders, and arm motion, you then can tell the direction the ball is being thrown.
Reaction to the ball is the ability to move at the proper angle in order to break up the pass. Don't round corners and angles. Your secondary drills must emphasize the ability to go to the ball and intercept it. Make the interception at the balls highest point. After making the interception return the ball to the nearest sideline, and if in traffic cover up the football. If a teammate intercepts the football, block the intended receiver if you are close enough.
If your secondary player has underneath zone coverage, then try and get a piece of the receiver as he travels through his zone. While bumping the receiver, the defender gets turned around, be quick to get vision back on the quarterback and squared up to play the football. Keep shoulders square to the line of scrimmage.