Know the differences between microphones. There are typically two types of microphones sold for live vocals, a dynamic and a condenser microphone. A dynamic microphone is the better choice for boosting live vocals. It will boost mid-range frequencies so that vocals can be better heard. A condenser mic is better at picking up high to low ranges, but has an overall flatter sound.
Don’t use reverberation, or reverb. Reverb may seem like it would boost live vocals, but it will only muddy the mix, especially if you are playing in a small bar or club. Most rooms have enough natural reverb to carry a semi-professional or professional vocalist. Instead, use delay in the mix, or a delay pedal to give vocals a full sound.
Hold the microphone close to your mouth. If you hold it too far away from your lips, the vocal levels can become erratic. This can also cause all kinds of noise to bleed through, such as crowd noise and feedback from the monitors. You want only your vocals going through the microphone.
Keep vocal monitors as far away from the microphone as possible. Placing monitors behind the microphone, instead of the front of the stage will greatly reduce feedback and amplify vocal gain.