A work like The Handbook for Working Singers provides practical information for the professional vocalist. There are chapters on live, choral, and studio singing. There are others on performing, touring and vocal fatique and even on overcoming stage fright.
Books like Find Your Voice, The Singer's Companion, and The Performer's Voice take a holistic approach looking at "vocal mechanics"--how the vocalist's or speaker's entire body can be used to produce a full and beautiful tone. These titles look at how the bone and muscular structure, larynx, chest and vocal cavities all interact to produce the vocal tone. The latter two titles also look at vocal health--issues like sleep, nutrition, exercise, and how to cope with illness and hoarseness.
Singing and Communicating in English is a meticulous explanation of precise vocal diction. This work looks at the interaction of the larynx, vocal cavity, tongue and lips and provides charts and drawings that explicate proper pronunciation. It also provides exercises to help the vocalist or speaker perfect their pronunciation.
If these titles are too difficult and technical there's always Hit Me With Your Best Shot: The Ultimate Guide to Karaoke Domination. This book says very little into vocal technique, but instead focuses on many extra-musical aspects of performance working the set-up of equipment, the room, dancing to the music, etc... It also includes repertoires of songs to help singers to express themselves.