Diaphragmatic breathing is very effective with helping your voice.
a) Stand against a wall with your head, shoulders and bottom touching the wall.
Place one hand on your midriff and one on your chest.
b) Breathe out to remove as much air as possible from your lungs.
Your midriff area should move inwards but the hand on your chest should not move.
c) Now breathe in steadily through your mouth and your midriff area should move outwards.
As you breathe out, your lungs reduce in size and your diaphragm moves up and thus your stomach moves in.
d) Repeat this exercise a few times.
Once you have got the hang if it, you can take a few diaphragmatic breaths before you begin speaking.