The diaphragm is a muscle located between the abdominal and thoracic cavities. The diaphragm is responsible for pushing out air that is sufficient enough to project the sounds you make, so exercising the diaphragm is crucial to vocal projection. There are many ways you can do this. One of the easiest for beginners is to take as much air into your lungs as possible, breathing deeply until they are filled. Slowly exhale, letting the air out, then try again. Do this several times. When you feel you're taking enough air into your lungs, begin singing a single note. Unless you're already accustomed to using your diaphragm to push the air from your lungs, your voice will sound weak and the note will falter. You're probably singing from your throat, which doesn't allow you to project your voice at all, and can do damage to your throat. Fill your lungs by breathing in through your nose and mouth simultaneously, then concentrate on the area just beneath your ribs, where the diaphragm is located. Keep working at it until you are using that muscle to push the air from your lungs.
Controlled breathing exercises can help make using your diaphragm more natural. Try deep, slow breathing exercises to accomplish this. Breathe in through your nose and fill your lungs, then breathe out slowly. Quickly releasing your breath doesn't give the diaphragm time to think about what it needs to do. Breathing out very slowly will force your diaphragm to take control and prevent the breath from escaping. Mastering this technique helps give you control over your diaphragm and strengthens too. Do not suck your stomach in after performing this exercise. Allow it to come in slowly and naturally. Sucking your stomach in is a sign that you are not using your diaphragm properly. The belly should remain relaxed while you take in air, but not forced out. The exhalation should be more like allowing the air to gently release, not actually pushing out either.
Singing scales is not only excellent ear training, but scales can be used to practice vocal projection. Start on the first note of the scale you want to sing, breathe deeply through your nose and mouth simultaneously, and begin singing the scale, pushing each note out progressively louder. Use the air and diaphragm: Never push with your throat. Practice releasing your breath slowly and evenly behind each note in the scale. By the time you reach the last note, it should be loud, clear and solid. If your voice is cracking, you aren't using your diaphragm to push the notes, or taking in enough air to sustain the notes. Try this same exercise lying on your back with your hands on your waist and your fingers positioned right at your navel. If you are using your diaphragm properly, you will be able to feel vibration beneath your fingertips.