In his first book since the enormously popular Great Singers on Great Singing, the distinguished Metropolitan Opera basso Jerome Hines here provides a wealth of new information and advice for all those who have embarked on - or plan to embark on - a serious singing career. From basic information on how the head and body combine to produce vocal sound, he goes on to analyze the ''four voices'' encompassed by the singer's one voice, always explaining how through proper technique and training that voice can achieve its ultimate in power, grace and beauty. On another level, Mr. Hines guides the singer through the labyrinth of choosing the right teacher, shows how physical and emotional health and care of the body relate to the vocal apparatus and considers such diverse matters as stage fright, dealing with conductors and managers and that final challenge - facing the critics.