I have provided links on this subject in another thread discussion of singing.... let's see if I can remember them!! Well, they are at the bottom of my voice teacher's homepage, so it's easier to give her URL:

Suzanne Gorder
http://www.mcn.net/~gorders/index.html

The link on the page above to the Center for Voice Disorders includes tips, such as warming up. As far as breathing, I had heard in school all my life about 'breathing from the diaphragm', but no one ever really explained to me how to do that until I started taking private lessons. The important technique about breathing is to develop the muscles at the floor of your abdomen, so that you can hold those down as long as possible while you slowly control the release of that air through your vocal chords. Warming up correctly is an important part of preventing vocal strain. There are alot of important techniques, and they are covered for the most part by the links at the bottom of Suzanne Gorder's page. Another important thing to remember is to not push your voice in ranges that are unnatural for your vocal chords.

Alice in Montana