Movements of Touch

Ample preliminary movements to the key are to be implemented, by setting out to reach the key prior to the point in time in which it must be set in motion. These preliminary movements are helpful in achieving a continuous sense of motion.

The right way is to reach the keys always quite gently with your finger-tips. The resistance of the key can then be gauged on the way down. Whereas, the incorrect way is to "lift" the fingers, in such a manner, "that the key may be hit down" which is the incorrect way of setting the keys in motion.
Remember, it is only after your fingertip has reached the surface of the key that the tone-producing action must "follow-on." These two distinct activities of

1. reaching the key and
2. bringing the key into motion.

can be combined into one physical motion.
The finger-movement to the key should always be quite light. The tone-producing action after key-contact may involve a stronger exertion of the flexors located in the forearm.

Thus, for instance, when you turn your hand over into its playing position, your thumb reaches the key-surface quite gently. But to sound its note, the forearm rotation as well as the thumb exertion must be increased during the moment of key descent.
The movement during key-descent may, in this case, be either a movement of the thumb, or of the forearm rotationally. I normally use forearm rotation to forearm rotation to set a key in motion when I play a note with the thumb. Movement of the thumb results when its exertion out-balances that of the forearm.