What are the vital techniques for singing while playing the piano?

A、While pressing down the keys, our fingertips have already touched the key.;

B、The speed pressing down keys should go from fast, to slow pace.;

C、While playing a vocal phrase, we should fulfill the transfer and transmission of arm weight between fingers.;

D、The speed of pressing down the keys, changes from slow to fast, besides, leaving the keys should be slow.