The primary task of any index is to direct the reader to a specific topic. It is used for a quick reference of particular topic or keyword. A good index has and needs Accuracy, Depth, Conciseness and Logic. Index creation needs understanding of the subject as well as potential users. If as an author you have all these qualities, and can cope deadline pressure, than you are the best indexer for your book. Otherwise: Entrust your index to a professional indexer
Professional indexers use subject knowledge with indexing skills to create good index.
A professional indexer structures the index in such a way that the reader can view the connections between and among various concepts.
A professional indexer highlights not only the express ideas found in the text, but also those that are merely implied.
A professional indexer uses key terms and phrasing that will lead users to the place in the text where the concept is discussed.