Don't force yourself to sing if it hurts. Instead, vocalize just under the volume where your throat starts to hurt. This will gradually strengthen and stretch your throat, allowing you to increase the volume slowly.
Maintain a healthy lifestyle by eating healthy and quitting smoking. Smoking will wreak havoc on your throat and vocal chords, causing it to sound scratchy and leaving you out of breath. A healthy diet will help strengthen your vocal chords, making them more resilient and less likely to develop nodules, which are small swellings in the throat that can develop from overuse.
Don't sing out of your range. Just like a weightlifter should never lift more than he is able, you should not attempt to sing notes your throat cannot handle.
Warm up before every session. Just as you need to warm up your body before a physical workout, your will need to warm up your throat for a vocal workout.
Rest your voice for a few days if you notice pain. Contact a professional vocal instructor, who can help you begin speech therapy and proper singing exercises.
Avoid singing in dusty or smoky environments, such as nightclubs. The dust can irritate your throat and lead to pain after a while.