Breathe from the diaphragm to ensure proper air support. When breathing from the diaphragm, be sure your lungs and sides expand with air. You can feel this by placing your hands on your waist as your hips expand.
Warm up properly by buzzing with your lips on the first five notes of a major scale, starting on middle C for sopranos and altos or an F if you are a tenor or bass. Ascend and descend the scale and then move up by half steps to continue the sequence.
Sing long tones to help improve your timbre. Long tones will help build the strength in your voice and enable you to obtain a clear, more focused sound.
Sing the same five-note scale you buzzed, but this time sing an "ah" sound. Start on middle C if you are an alto or soprano and a fifth lower if you are a tenor or bass. After each five-note series, start a half step higher and continue singing as high as you can.