plan your query in a way that makes sense
write your concept outline or map
Why make this outline or map as your first step?
Medline will try to help you find search words for you to use!
Use them if they make sense in the query.
Other databases will assist you in the same way. (It may look different, but they'll offer a way to find additional keywords.)
You can also add countries/regions/ethnicities to the end of search concepts.
Sometimes you can even use the Topic Finder tool to help you map out your query!