Here are some rule interpreta- tions concerning serving that you might find useful.
SITUATION: A server on Team A called the score but before beginning her service motion, the receiver on Team B called a time-out. Team A claimed Team B committed a fault because a receiver may not become “un-ready” after the score has been called.
QUESTION: Did the receiver on Team B commit a fault?
ANSWER: No. It’s generally true that a receiver may not become “un-ready” after the score is called (Rule 4.C.2), however, there are a few things which may occur after the score is called but before service motion begins. One such thing is any player may call a time-out before the service motion has begun (Rule 4.D.2).
QUESTION: Can a server tap the ball with their paddle after the score has been called? I have a partner who taps 2 times as part of his serve routine. We are playing in a tournament in a few weeks and want to make sure it is a legal serve.
ANSWER: Of course, he can. And as you are describing it, the taps are before your partner starts his service motion, so there is no problem.
QUESTION: After announcing the score, is it legal to do a practice swing before actually serving the ball?
ANSWER: The server is not allowed to take a practice swing or fake a serve. Unless a hinder has occurred to cause the server to not contact the ball, the referee will call a service fault (USAPA Casebook for Referees).