I have read and re-read this book in its entirety, and in my view is invaluable if you want to become a more confident writer/performer or just want to have a deeper understanding of what humour actually is. The author offers many exercises for the reader to complete. This built up my confidence and made me realise that you can make a whole bunch of boring and mundane parts of life into supremely comedy sequences.
First the basics of what makes us laugh are explained. The book then moves into defining how to make your comic characters and to forget about why you think a certain aspect is unfunny.
After this the book is split up into seperate sections depending on which field of comedy you wish to pursue, be it sitcom, sketch, stand-up, and, ahem, practical jokes (it is hard to show sarcasm through text).
The end of the book applies to every comedian, helping you to perfect your work, and ultimately selling your material.
Unfortunately the book is not prfect throughout. Most explainations of certain comic situations involve the use of a 1980's film or tv series, so if you are under the age of, say 25 like me (or, if you didn't watch American shows of the 80's) I would strongly suggest buying Mel Helitzer's Comedy Writing Secrets, 2005. Apart from this I strongly recommend this book, trust me you can't go wrong.