Make a list of keywords and phrases that describe your topic.
The words you use to search in indexes and databases (including Google) may determine whether you are successful in finding information. When searching full-text, especially for historical topics, consider alternative terms and spellings, e.g. "callico" and "Kashmir." As you skim through records for books and articles, keep building a list of search terms that will potentially yield results.
Most databases let you construct a Boolean search using AND and OR.
Focus a broad topic by stating your topic as a question.
One way to "frame" the question is to apply some of these four parameters: time, place, person/group, event/aspect.