This is what I learned as proper etiquette for the USTA 10 minute tournament warm-up time:
Flip coin or racket spin first and determine side/serve.
~2 mins short court groundies (let ball bounce, not volleys)
~5-6 mins full court groundies, middle court and cross court
~1 min each at net volley/options (ask for overheads etc)
~2-3 mins serve to each other 3 balls at a time, catch balls unless you ask to return.
Does this sound about right?