Boil your topic down to the most important words. Ignore superfluous words like in, the, of, with, against, affect, impact. Begin with a keyword search--Select a Field (optional).
Put each "different piece" of your topic in a separate search box, if available. Using the topic of experimentation with instructional methods or training for PDD-NOS as an example below, note how each different piece of the topic is entered on a separate line. Synonyms for the pieces are connected by OR--and kept on the same line--as seen below...
Too many results? Focus your search by searching for your keywords in the ABSTRACT field or the TITLE field. Click on the Select a Field (optional) pull down bar to select the abstract or title field. Or...change your topic slightly--in this case, you might want to look at just PDD-NOS.
Too few results? Think of synonyms. Add synonyms to your search--using OR--and keep your synonyms all on the same line.
Increase your results by removing the least important "piece" of your search while still retaining the "essence" of your search, if possible. In the example above, both pieces are pretty important.
Still no results? Broaden your search slightly. "Pervasive Developmental Disorders" might be another avenue to try. Still no luck? Try a different database.
When reviewing your results, look for relevant "subject" or "descriptor" words. Find subject terms either on the results page, or at the end of individual records. Write down relevant subject terms that you find.
Go back to the search screen and using the subject terms you discovered, search your subject terms in the subject or descriptor field. Subject terms are gold threads--they will almost always lead you to the most relevant results.