I have a non-fiction book that I want to create an index for.
Is there any standard for what items should be included in an index? Some things are obvious like names and proper nouns. But, is there any set of guidelines I can or should refer to in order to determine what defines a complete index?
What goes into your index will be defined by your readers' needs. How will they use your book? Will they come in with knowledge of (and vocabulary from) a related subject? Are they experts or novices or some of each? An index's primary job is to have an answer when somebody comes to it with a question.
Here are some guidelines that I've learned over many years of doing technical writing. I never formally learned this and style guides don't tend to cover indexing in any detail, so this is just one person's accumulated experience:
Index entries about operations get at least two entries, one for the noun and one for the verb. People might try to find out how to insert a whatsit by looking under either "inserting, whatsits" or "whatsits, inserting".
Use those index entries everywhere they're relevant, not just the first mention. For example, do you have a "troubleshooting" section that covers problems with inserting whatsits? Index that; if somebody's having trouble inserting his whatsit, you want him to find that. If your index never lists more than one page number for an entry, you're probably missing something.
Standardize your verbs early. You don't want to have some of your entries under "inserting" and others under "adding", unless there are precise technical differences between the two. If there are such differences, consider see-alsos under the two verbs. As for which verbs to use, I know this sounds circular but you want to use the verbs that your readers will naturally reach for, so there's a "know your users" issue here.
Index concepts (things people need to know, as opposed to things they'll do) if your readers might reasonably need to look that up, but not if it's passing or unimportant. Don't fill up your index with too much "just in case" entries; they make it harder to find the ones people actually need. (In a digital copy you can be more generous because people can search, but for paper, make it easy to use.)
Find some way to test your index. Nobody ever seems to review those carefully, but maybe you can do some informal user testing. If you have access to reader feedback after release (bug reports, for example), look closely at the ones where there was documentation but they apparently didn't find it.
In my experience gerund verbs and plural nouns are most common as index entries.
What goes in your index will be defined by your topic.
A book on prefixes will list prefixes. Other books won't. Names of authors of scientific papers don't usually go into the index, but historical figures will. And so on. You might even have words in your index that don't appear in your text but are different names for the same thing (e.g. Latin plant names, if your text uses common English names).
Don't just blindly index all names and nouns, think about what the readers of your book might be interested in.
From experience I would suggest as much as possible. Many writers/editors try to be smart and reduce the size of the index, but then you end up looking for something you know is in the book, but you can't find it. If you want include a qucik index with the most common or prominent items too.
The other thing is the TOC, I would suggest two versions there two, a quick TOC on 2 pages max, where you just see the main headers. And a little longer one where you can see everything in detail.
Nothing is worse than having a good book that you can't use properly, and people are used to full text search from almost every computer program, so you should have at least the possible paper equivalent of that.
