I have a number of resources on singing technique, of which Jeffrey Allen's Secrets Of Singing has proved to be the most useful. Vocal Workouts starts with some basic info on how to approach singing and practice, how to warm up physically and vocally, mental approach (part of which I found enlightening), what to watch out for and so forth. Then there are a number of exercises in different contemporary music idioms. I found some of the exercises a little difficult to follow and wasn't always entirely sure about what I was aiming for. However, this title did add to my practice - at the moment I am using a combo of class and private (book-led) practice, as I don't have money for private tuition, and I am seeing results!