Make sure when you breathe you connect with your belly (like when you sigh) - and try and keep the back of the tongue down and some space between your back teeth. The space in your pharynx, mouth and the front of your face (nasal cavities, sinus etc.) all amplify the vibration from the vocal chords so more space is more volume. Try to sing on open vowels - m, n and the ng sounds (eg something, singing etc) are not as loud as the open vowels.