Check your breathing. Sing a note while placing your hands on your sides. If you do not feel your sides expanding, then you are not breathing correctly. Aim to take in air deeply by ensuring that your stomach, sides and even back expand with air.
Learn proper diction for consonant and vowel sounds. If you are not using proper diction, your audience will not be able to understand your words. Diction will provide you with the knowledge to pronounce words correctly in relation to singing.
Relax any tension in your neck, throat, jaw, back and shoulders. Tension in any part of your body will negatively affect your singing voice. The vocal folds must be able to vibrate freely and without any obstructions. When you sing hunched over or with tension, the vocal folds do not vibrate freely. For this reason, stand up straight, keep your neck open and relaxed and keep your jaw slightly down.
Pay careful attention to any stress in the vocal folds and throat area while singing. Keep your tongue relaxed and avoid singing notes which are too high or too low in your voice. Singing too high or low can damage the voice.