Chanting is said to be "breath made audible," and learning to breathe well is the first step in learning to chant.
Sit up straight. This allows your lungs to expand more fully.
Place one hand on your lower abdomen.
Feel your belly move as you breathe ... in and out ... in and out.
Make sure that your belly is expanding out as you breathe in. You can make sure you're doing this correctly by noticing if your hand is being pushed outward away from your spine.
As you exhale, your belly should contract, your hand settling back toward your spine. Try this a number of times.
Now, breathe again into your abdomen. After your belly completely fills with air, only then allow your chest to fill with air as well. Experience your breath like a wave, filling up your belly then rolling up into your chest. And as you exhale, let the wave begin in your chest, emptying the air from your lungs and then rolling down into your abdomen, until your abdomen is fully contracted and empty of air. Do this several times.
Now try removing your hand, but continue breathing and remembering the feeling of the air pushing your hand out and in.
As you continue with the exercise, gradually deepen your breathing. Without any sense of pushing, slowly increase the volume of air coming into your belly. The deepening of breathing should come from your belly - the chest is more like an afterthought.
Do this for several minutes, deepening and relaxing into your breathing. Feel the waves roll in ... belly up to the chest ... and roll out again ... chest into the belly ... letting go of effort ... letting the waves of breath breathe you.