Kalstolyn
make sure you make a lot of space in your mouth, as if you were yawning. and try not to "shout-sing" or you can hurt your voice.
I second this.
I learned that it helps to keep the sound well supported and also focused too, like not too spread out. I used to be a really breathy singer, but in the past few years in choir it's helped me sing a lot clearer and audible.
