There are a couple more hints for finding related subjects for your seaches, assuming that you've had a least one successful search with a few relevant articles. On the left hand side of the search results screen, you'll see another box titled "Subject: Major Heading":
This box lists the subjects that are in the article that are listed to the right in the search results. Clicking on one of these boxes will only narrow your current results- HOWEVER- this is good list to look and see if there are some better/alternate subject headings you could use for a new search.
Additionally, on good article can lead you to a whole host of clues. If you find the perfect article, click on it and you'll see the article record. This record also includes a list of major and minor subjects used to index your article:
You can click on one of these subjects to execute a new search on that subject heading, but realize that the search uses only the subject heading you clicked on; no limiters or additional terms are included in that search. It might be best to modify your current search by copying-and-pasting a new subject into it.