When athletes perform a tuck jump, they start in the "athletic position" with feet shoulder width apart. From a slight crouch the athlete swings the arms behind and jumps straight up. The knees are pulled up as high as possible and tucked under the bottom.
There are several common mistakes athletes make when completing the tuck jump.
Athlete doesn't start in the athlete position; legs are too close together or too far apart
Thighs aren't parallel to the floor at the top of the jump
Legs are not together during the jump
Athlete lands with the feet too close together or too far apart
Athlete doesn't land on both feet at the same time.
Athlete lands with one foot in front of the other
Videotape yourself and see if any of these are occurring when you do this jump. Pick one area at a time to work on. When you can see the desired result on videotape, choose the next problem and perfect that. Make sure each component remains as desired while adding each new movement.