When to serve or receive
As everyone is so pressed about the Serena-Jankovic when to serve incident. Here is the official rule form the rulebook it is on page 448.
21. WHEN TO SERVE & RECEIVE
The server shall not serve until the receiver is ready. However, the receiver shall play to the reasonable pace of the server and shall be ready to receive within a reasonable time of the server being ready.
A receiver who attempts to return the service shall be considered as being ready. If it is demonstrated that the receiver is not ready, the service cannot be called a fault.
22. THE LET DURING A SERVICE
The service is a let if:
a. The ball served touches the net, strap or band, and is otherwise good; or, after touching the net, strap or band, touches the receiver or the receivers partner or anything they wear or carry before hitting the ground; or
b. The ball is served when the receiver is not ready. In the case of a service let, that particular service shall not count, and the server shall serve again, but a service let does not cancel a previous fault.