Warm up with some gentle scales and phrases at low volume before singing. Gradually increase the volume and complexity of the phrases and scales as you go along. Concentrate on how your voice feels and pay attention to your throat, avoid straining or placing excessive pressure on your vocal chords.
Coat your throat before performances by drinking beverages with honey. Avoid high-sugar drinks as they can make your saliva thick and syrupy, which impedes the vibration of your vocal chords. Hot drinks before and after you sing can help relax the chords and increase the effectiveness of your warm ups.
Avoid smoking at all costs. Cigarette smoke is one of the single worst things for your voice. It is a powerful expectorant that dries the throat and causes your vocal chords to tighten. This reduces your effective pitch range and increases the amount of wear on your throat when you sing.