The first edition of 'Creative Photoshop' was, I believe, one of the most useful Photoshop books ever published, each chapter opening up a new way of using the program.
If you don't own the first edition I'd say this is an essential purchase: the new edition contains all of the chapters in the first edition, plus four new ones, 19 tutorials in all. Each provides a detailed step-by-step guide to the process Derek followed in creating a particular type of illustration. And I mean really detailed: every step is explained exhaustively and illustrated where necessary with relevant screenshots of the Photoshop interface - you see exactly how each effect is accomplished.
Derek makes use of a exceptional range of Photoshop tools through the book, and by the end you'll have an excellent understanding the application's more sophisticated features, such as channels, the pen tool, the shape tool, selection tools and masks. The blend of bitmap and vector is a characteristic of Derek's work, and the book makes clear how these different sides of Photoshop can be combined to create striking and novel effects: one fascinating chapter combines medieval 'woodcut' design elements with smooth vector lines and shapes to stunning and original effect - looking like something Durer might had come up with had he had access to Photoshop.
If you own the first edition you will also want this one as the four new chapters are of the same quality as those in the original, and cover new illustration concepts, including sketch and dry brush effects, screen-printing and collage. The new edition also contains new images from Derek's portfolio.
The book can't supply the imagination and aesthetic sense you need to create illustrations of similar quality, but it opens the door: in addition to detailing the Photoshop techniques used to create each piece Derek explains how and why he chose its source materials, and discusses what constituent elements are likely to work well together.
A great introduction to digital art, still in my view the best.