One way to limit your search to particular fields is by using field tags, such as [ti] to search a title word, [au] to search an author name word, [ta] to search a journal title word, etc.
Example: "food desert"[ti] searches for this phrase in the article title.
A complete list of all PubMed field tags as well as description of each is available from PubMed Help
Different results displays give you different information. Click on Summary for additional formats (above the results list).
Finding the Medical Subject Heading (MeSH) term for your search topic can often retrieve more relevant results and help ensure that you don't miss articles.
There are two ways to access the MeSH database.
NOTE: Not all concepts are represented well in MeSH. If you cannot find a relevant MeSH term for your topic, try searching for it in the title. For example, "life course" [ti]
MeSH terms have a variety of subheadings that you can use to focus your results more precisely. Some useful subheadings for public health include: epidemiology, prevention and control, and statistics and numerical data.
If you are still getting too many results, another way to focus your results is to make the MeSH term the main point of the article. To do this, check the Restrict to MeSH Major Topic box below the subheadings list. Or, in the search box, replace the [mesh] tag with [majr].