Warm up your voice before singing, and before you go about your busy workday, where you will be using your voice at full strength. Even on a minimal vocal day, you should start with a light hum that “floats” between registers and transitions the break over and over; the shower is a good place for this, since there is warm moist air to work with. For a singing engagement, you should never go into it without a thorough 20 minute workout.