Add vocal exercises to your daily routine. It is not enough to simply practice singing, you should engage in vocal exercises daily to help strengthen your singing voice. Try basic warm up exercises that use little breath and help you with scales. It is also a good idea to cool down after singing as well.
Do exercises that help you breathe in a controlled manner. Begin with slow breathing. Inhale slowly counting to 20 and then exhale just as slowly counting backward from 20 to 0. This can strengthen your singing voice by relaxing your vocal chords and helping you use your diaphragm.
Improve your posture and strengthen your singing voice. You must work on your core muscles, and back muscles, to help with good posture. In order to breathe correctly when singing, you must have a your lungs stretched to their full capacity and not pressed down by a slouching spine. Pilates exercises are great for strengthening your abs and core muscles.
Include relaxation exercises with your vocal ones. In order to have a full vocal range, you must be able to rid your upper body of tension Aerobic exercises or jogging can help you release energy before you begin singing.
Work with a reputable vocal coach to learn the proper way to sing and strengthen your singing voice. The proper technique can help you find your fullest range and prevent straining your vocal chords.