Problems with forward slips are showing up. Some applicants are starting the slip with a skid and then trying to correct to the slip. Skidding an airplane at low airspeed and low altitude is dangerous and will wake me from my nap!
The "forward slip" is a slip in which the airplane's direction of motion continues the same as before the slip was begun. If there is any crosswind, the slip will be much more effective if made toward the wind (wing down into the wind). Slipping should usually be done with the engine idling. There is little logic in slipping to lose altitude if the power is being used.
Assuming that the airplane is originally in straight flight, the wing on the side toward which the slip is to be made should be lowered by use of the ailerons. Simultaneously, the airplane's nose must be yawed in the opposite direction by applying opposite rudder so that the airplane's longitudinal axis is at an angle to its original flightpath. The degree to which the nose is yawed in the opposite direction from the bank should be such that the original ground track is maintained. The nose should also be raised as necessary to prevent the airspeed from increasing. These are very smooth, fluid control movements.
If a slip is used during the last portion of a final approach, the longitudinal axis of the airplane must be aligned with the runway prior to touchdown so that the airplane will touch down headed in the direction in which it is moving over the runway. This requires timely action to discontinue the slip and align the airplane's longitudinal axis with its direction of travel over the ground before touchdown.