Use good posture when singing. You should stand tall with your back straight, your shoulders relaxed and your head facing forward. Don't lock your knees, as doing this causes some people to pass out.
Breathe deeply when you inhale before singing and release your breath in a slow, controlled manner as you sing. Try to take breaths at points in the music that allow for a brief pause, such as at the end of a phrase.
Tighten your abdominal muscles as you exhale while singing in order to control and support your breath.
Use your mouth properly. Relax and drop your jaw as you sing. Create as much space as possible inside your mouth to allow for maximum reverberation and pleasant tone. Also, lift your soft palate. This is the soft area on the roof of your mouth, in the back toward your throat.
Warm up slowly. Sing softly and practice some scales or simple songs first before building up to louder volumes. This can help to prevent vocal problems such as hoarseness.
Enunciate properly. Make sure to pronounce your consonants sharply and crisply. Use open vowel sounds. Instead of the typical short "a" sound as in "apple," sing "ah-pple." Sing an 'i" with an "ee" sound, and a "u" with an "oo" sound.
Learn your music. If you don't know how to read sheet music, learn at least the basics. Follow the notes carefully to see if they rise or fall in pitch and to see how long you should hold them.
Watch the director very carefully. All eyes need to be trained on the director or conductor in order for the sound to be uniform and harmonious.
Blend your voice with others' voices when singing with a group. Ideally, no voice should be louder or softer than any other.