To find information in a book or database, you must identify some useful keywords (aka words or phrases) to look for in an index, table of contents, or to use in a search.
You use keywords to locate information on concepts. In this context, a concept is a thing, person, place, cause of action, defense, idea, etc. etc. which can be described using a variety of different words or phrases.
Steps to Identify Useful Keywords
Basically, you just ask yourself, what are the different words/phrases that a JUDGE might use when writing an opinion, a LEGISLATOR might use when writing a law, or an AGENCY might use when writing a regulation.
Examples
There are acronyms such as TRAPP to help you think of concepts/keywords of legal or factual significance from your issue/fact pattern.
T - Things involved
R - Relief sought
A - Causes of Action or Defenses
P - Person or Parties involved
P - Places