1. Always warm up before you sing. However, if this isn't possible, pick a song that is easy on your voice and use this song as your warm-up exercise.
2. Don't sing songs that hurt or strain your voice.
3. If you can afford it, take voice lessons. Proper training will go a long, long way, even for the most naturally talented of singers. Lessons can help prevent damaging your voice as well as help you to find your true voice potential and develop good singing habits. If you have ever had problems speaking the day after a Karaoke event, you are hurting your voice and thus a prime candidate for lessons.
If you have trouble making it through a song and you are not sick you really need the assistance of a voice coach.
4. Do not sing with a sore throat. Not only can you hurt your voice, but you could pass your illness on to others via the microphone.
5. If you feel your voice is straining during a particular song you should see if a key change by the KJ helps make singing that particular song easier. Most people aren't aware that this can be done.
6. If you feel the need to use throat lozengers throughout an evening of singing, and you are not sick, you also are in need of vocal training. This is another big sign you are singing improperly and are hurting your voice.