Read "Winning Ugly" by brad gilbert. like "chatt town" says, preparing yourself from the match begins before the match begins. Its in how you prepare your game plan, to nutrition, to warming up, to bringing enough equipment with you to the court. Then theres the aspect of keeping your feet active... don't plant your feet into the ground, you'll be late for everything. Brad calls it "happy feet". dance around on the balls of your feet. Make sure you split step EVERYTHING.
Like for me, I always forget to split step after I serve when I'm returning my opponent's return of my serve. I'm always caught off guard and it makes me lose some service games because of it.
winning a match has to do with literally EVERYTHING you do from before you get into your car to the way you're breathing while on court. if you slack off, forget to do a few things, then before you know it -- you're down a set and can't break your opponent's serve.