Indexing is not for the faint of heart. It requires superb mental organizational skills, and an ability to discern the big picture while sorting out the minutiae. Without proper organization, you might go mad.
Especially with academic books, organizing topics can be a seemingly impossible task, but clear thinking and the ability to organize and keep a mental “topic tree” can help immensely.
Think of the topic tree as having one trunk, the overarching topic of the manuscript, and numerous offshoots of branches. These branches are the key topics of the book, and on each major branch you might have offshoot branches of subtopics. Possibly, you might have smaller offshoots, which you can envision as leaves (most publishers prefer not to have triple embedded subtopics).
Once you define the trunk, for example The Massachusetts Bay Colony, then you begin to identify the main branches: history, historical personages, laws, church-state relations, Establishment Clause, Mashpee Plantation, etc. Off of each of these branches, you would construct subtopic branches, such as the personages involved in the establishment of the colony, or important moments in the history of the colony.
The secret to building the topic tree is the ability to categorize mentally as you read through the manuscript. There are simple steps to follow in order to create the topic tree.
First, you should never begin indexing without first studying the Table of Contents. The TOC will give you an excellent idea of the main topics of the book. These won’t be the only main topics, but they are a good place to begin. Take notes off of the TOC and use the chapter headings as your first main branches, and possible offshoot branches.
Next, read the book. Take copious notes on your initial topic tree outline, adding to it and fleshing it out with subtopics and, possibly, sub-subtopics. Nothing is set in stone at this point, so write down all the topics and subtopics that occur to you.
Once you have read the book, look at your drafted tree and see if you can identify connections, where topics might actually be subtopics of a larger branch.
Find any dead branches, topics that might not be important in an index, such as examples that have no bearing on the larger subject of the book.
Eventually, after your second read-through, you will have a working topic tree, and you can begin to finalize its design and assign numbers to the topics.
Slow, steady, and organized—that is the only path to indexing success.