Even if you already have a great voice you aren’t doing it any justice if you haven’t learned how to properly breathe or warm up. If you learn every technical aspect of singing and then apply what you have learned to your practice, you will quickly feel and hear a significant improvement.
Any great singer or vocal coach will tell you that learning how to properly breathe is one of the most important things you can do. You will never be able to hold those notes and journey out of your comfort zone if you don’t have the breath to supply you with power and control. It is essential that every time you warm up that you place your hands on your abdomen and practice breathing in and out without moving your chest.
Working on your posture must be done every time you practice as well. It is a good idea to spend some time singing in front of a mirror or if you have a camcorder, you can record yourself. Evaluate how you stand. Do you start to slouch halfway through the song or pull your chin in when you try to sing low notes? Ideally, your shoulders will be back but all of your muscles in your body should be relaxed. Your head needs to be up with your chin level and your knees should be loose.
Another good warm up exercise is to stand relaxed, take a proper breathe and sing a note. Hold this for as long as you can. Play with this exercise a bit by holding your mouth different ways and singing a variety of notes.
It is also important that you learn how to remember songs. Sometimes even just learning one song can be tricky enough if you are not familiar with it but what if you have to learn a whole set or a musical? There are cues to learn, lyrics to memorize, etc. Reading the song out loud and repeating it super fast over and over again is helpful as is writing or typing out the words while you say them. There are quite a few vocal singing exercises you can do to learn lyrics. It is usually just a matter of determining what works best for you. Always remember to find meaning in the song that you are singing so that you can really connect with it and then deliver that in your performance.