Consider the following:
As you consider your topic, begin categorizing it into concepts, keeping in mind:
To demonstrate each step, we'll use the following topic:
Which interventions, and more specifically, what factors in those interventions result in the reduction of the use of tobacco products, especially cigarettes, among adult African Americans?
If you break the topic apart, what are the primary concepts in the above statement? What are synonymous terms for each of those concepts?
As mentioned before, 3 is a magic number when developing concepts. If you can come up with 3 separate concepts, then you will find that your search is more organized and easier to understand. The other benefit is that you can more easily edit your search if you are using an interface such as Ovid.
Sometimes the third concept is a study type but more often than not you can use the study type to limit results rather than as a concept in and of itself.