1 Overcontrolling the antitorque pedals, which not only changes the handling of the helicopter, but also changes the r.p.m.
2 Reducing throttle rapidly in situations where proper r.p.m. has been exceeded. This usually results in exaggerated heading changes and loss of lift, resulting in loss of altitude.

HOVERING
Hovering is a maneuver in which the helicopter is maintained in a nearly motionless flight over a reference point at a constant altitude and on a constant heading. The maneuver requires a high degree of concentration and coordination.
TECHNIQUE
To maintain a hover over a point, you should look for small changes in the helicopter’s attitude and altitude. When you note these changes, make the necessary control inputs before the helicopter starts to move from the point. To detect small variations in altitude or position, your main area of visual attention needs to be some distance from the aircraft, using various points on the helicopter or the tip-path plane as a reference. Looking too close or looking down leads to overcontrolling. Obviously, in order to remain over a certain point, you should know where the point is, but your attention should not be focused there.
As with a takeoff, you control altitude with the collective and maintain a constant r.p.m. with the throttle. Use the cyclic to maintain the helicopter’s position and the pedals to control heading. To maintain the helicopter in a stabilized hover, make small, smooth, coordinated corrections. As the desired effect occurs, remove the correction in order to stop the helicopter’s movement. For example, if the helicopter begins to move rearward, you need to apply a small amount of forward cyclic pressure. However, neutralize this pressure just before the helicopter comes to a stop, or it will begin to move forward.