Good breathing is the beginning of a healthy trumpet sound. Ensure you have a good supply of breath by breathing deeply into your stomach. Controlling the blowing of the breath as you play is very important. This is mainly achieved through tightening your stomach muscles for support.
Embouchure, approximately pronounced "ahm-buh-SURE," is how your mouth meets the trumpet itself. Good embouchure consists of making a good buzz with your lips as you blow through them. Begin with pursing your lips as if about to pronounce something with the letter P. Then blow through the lips while maintaining the lip tension so that a buzz is the result. Steadiness of breath and consistency of lip tension will lead to good tone.
Use your tongue placed in a position to pronounce a T to act as a valve to start the buzz with your breath. Directly after the T motion of the tongue, blow for the duration of the note desired. Stop the note by either using the tongue again as a valve, or stopping your breath with your stomach muscles (this is dependent on the style of playing).