Incorporate a warm-up into your rehearsal routine. This helps avoid stress or injury to your vocal chords. You can hum, scat, sing a scale, and even perform stretches.
Control your breathing by engaging the muscles in your lower abdomen as you practice inhaling and exhaling. Instead of letting the air flow freely, control how much air you breathe in and out. This is also known as using your diaphragm as it's the key to better, more polished vocals.
Get enough sleep and drink plenty of water on a daily basis. Drink at least half your body weight in ounces of water each day in order to keep your body and vocal chords hydrated. Take naps during the day if you cannot get at least eight hours of sleep at night. If you're often tired or stressed out, rest and water can help improve the quality of your voice.
Exercise your vocal muscles daily. Some exercises include making baby-like noises or singing the words "me,me,me" using your entire vocal range.