Make a constant "ssss" sound for as long as you can that is stable in volume and the amount of breath being exhaled. Repeat ten times. Then carry out the exact same process but make the sound as loud as possible. Do this ten times and put aside five to ten minutes a day to practice these breathing techniques. They will help to train your diaphragm to handle tension and create a constant, controlled sound, especially helpful in holding those high notes.
Lie down flat on your back and position your hands on your waist so your fingers point toward your belly button. Try to breathe in right down to your abdomen so that you stomach expands; your chest should fill up last. Don't breathe in until you are ready to pop. The point of the exercise is to practice breathing from your stomach, which is vital for singers. Exhale all the built-up air over five seconds and repeat this process ten times. Carry out this technique about four times a day, for about ten minutes each.
Now, you know how to breathe deeply down to your abdomen and how to let out the air as slowly as possible but also constantly and smoothly. Do this so softly that you wouldn't blow out a candle a couple of inches from your lips or even make it flicker. After repeating this ten times, do another five repetitions, but this time hold a note as you do; mix up the notes for each attempt. For the next five raise the volume of your singing from silence to the mid-point of the volume you can achieve, before returning to silence. For the final five breaths occasionally change the tone as you sing. Breathing out slowly helps your diaphragm fight against the actions of the abdominal muscles. This exercise also helps to keep a constant pitch.
Breathing exercises will help prepare you for any performances, but there are more techniques to use as you sing. Tighten your abdomen and keep your throat loose and relaxed so lots of air can pass through; think of how it feels when you yawn. When they come, high notes won't force the sound by tensing your neck muscles--simply exhale a greater amount of breath.