Originally Posted by tennis tom
You've already warmed up or should have long before any serious competitive match. The pros "warm-up" for an hour or two long before the so-called beginning of the match "warm-up". Stick with the traditional warm-up routine and things will go much better if you're playing against a real player--if you're not it really won't matter because he won't know any better either. If you need to "practice" or warm-up your shoulder, hit your serves on a practice court before your match. If it's a casual match, arrange with your opponent that you want to practice your serve for a while and maybe he can practice his returns.
I'm definitely for a good warm up hit before the actual match and I do it when I can. However, it's not always practical due to either time constraints or weather (we're playing USTA indoors and I'm not a member where we're playing or there are no courts available).