You can narrow your search by "Keyword" by selecting the option in the dropdown box.
Once your search results appear, you can narrow your search using the limiters on the left-hand side of the screen. (e.x. author, age group, methodology)
Screenshots courtesy of American Psychological Association.
Using the Term Finder can be a good way to retrieve more relevant results. Simply type in the search term in the search bar to find the matching PsychInfo term.
Once you've found the matching term, you can select it or "explode" the term to find other related terms to add to your search.