An index, while never the glamorous part of any writing project, is essential to the readability and usability of longer non-fiction and technical works. Building one need not be a chore, but it should not be an afterthought either. Here's how to make an index useful to readers without it becoming an unduly large project:-
1. Understand the purpose of an index. An index is an alphabetical listing of key words and concepts in the text. It contains "pointers" to those words and concepts, which are usually page, section, or paragraph numbers. An index generally appears at the end of a document or book. This is distinct from a table of contents, a bibliography, or other supporting materials.
2. Begin with a completed text. If the text is not yet complete, you can still begin the process of building an index as long as the text has most of its final structure.