First, the creative aspect of the cook book is not so much in the book, but in the cooking. Creativity typically takes a backseat to communicating the useful technical information required to help the reader successfully replicate a recipe. Cookbooks certainly can be creative, but most of this is confined to the layout, organization, and photography in the book. Cookbooks are first and foremost, user manuals, though there is a special category of cookbook that is as much an art book as a manual.
Clarity in communication is important in a cookbook. For those with a lot of experience in the kitchen, the hard part of writing a book can be in determining the difference between what they know and what is known by the typical reader of their book. You want to ensure that cooking instructions are clear, concise, and can be easily followed. Of course, different books are written for those with differing levels of kitchen expertise, so the key is to make sure you understand what your audience does and does not know.
One method used by cookbook writers is to have the recipes tested by people with the level of expertise to which they are writing. This helps them to identify where changes need to be made for clarity or conciseness.
Photographs are a huge component of cookbooks. Not only to do they help the reader to visualize how a recipe is supposed to look when complete, they are inspiring and often beautiful to look at when done well.