Breathe from your diaphragm when singing to use a concept called diaphragmatic breathing. To do this, expand your stomach and waist area to increase the amount of air you are taking in. You will sing more powerfully when you breathe and exhale from your diaphragm using the muscles in your stomach to control the airstream.
Play middle C on the piano and match the pitch with your voice. Middle C is the white key directly to the left of the set of two black keys in the middle of the piano. Ascend by half-steps to the highest pitch you can sing easily. Do not go any higher than comfortable. Determine the pitch five notes below your highest pitch.
Sing your pitch that you found in Step 2. Sing the sound "hmm" down a fifth. Singing this exercise will expand your range, making it easier to sing high. Continue this exercise, each time ascending a half-step.
Sing a major scale which is comfortable for you to sing from bottom to top. Sopranos or altos can start on middle C. Tenors or lower voices, start on the octave below middle C. Begin with a normal volume crescendoing to the last note in the scale. Your lung capacity and ability to sing stronger will improve. Breath every four notes so you will breath after "F" and the octave "C."
Add a half-step to the scale each time until you can no longer complete a scale comfortably. Do not stretch your voice; sing only what is comfortable.