I have found this to be an excellent book. It has a long chapter dedicated to managing momentum swings in matches.
Coaching Tennis - Chuck Kriese
There are many, many details regarding how to approach each point and game based on the score.
One of his points is similar to Brad Gilbert's "happy camper / wounded bear" that mikeler mentioned. Your body tends to perform better when you are behind than when you are ahead. A specific recommendation that Kriese mentions is to play an aggressive point when you are one point behind (15-30, ad out, etc.).
He also recommends playing a "breakdown point" when you are one point ahead. Basically a safe drawn out point to force the other player to have to go for a risky shot. Many players will try to go for the kill when they are ahead and end up losing the momentum with sloppy play. He emphasizes that you cannot be tentative on a breakdown point - "big shots and safe targets" is the goal.
This one piece of advice alone has been very helpful to my daughter in USTA play. Having a strategy that focuses on each point has helped her stay in the moment and not feel as if she has no control over what is happening.