Recommended Reading
As with any subject, practice is of the essence. Before taking up any aspect of music, it must be done on the understanding that you have to have the time to devote to it. So many people do not take this into account and cannot understand why they don't progress or at least very slowly.
Daily work is necessary. Exercises for fingers and voice are a must. Pieces and songs come later after a technique is established. Unfortunately, most people want to run before they can walk. Good habits from the start are necessary. I usually advocate for children to practise before they go to school as after there is homework and not enough time for music. A little everyday is far better than a long session at weekends. Even adults could do technique before they go to work and leave the pieces and songs for later.
It doesn't matter what kind of singing you enjoy, technique is essential. Styles come later, whether it be classical, pop, rock, music theatre. It is the same for piano and recorders.
For music theatre a knowledge of the show, book and score is necessary for an understanding of the character. Mimicking another singer is pointless. Your voice is special to you and no-one wants to listen to a copy of someone else.
Exams are a good way of performing and gaining confidence as are concerts, small groups of like minded players, festivals, auditions etc.
Students must be able to take constructive criticism as well as praise.
A knowledge of music theory goes a long way and knowing another instrument is also helpful especially for a singer to learn the piano. In time they can accompany their own songs.
