Before you start entering any search terms, think of as many relevant terms and combinations of terms as you can. This will help you to avoid getting stuck in a rut with the first terms that come to mind.
Try the databases' Advanced Search feature, which usually gives you the ability to search multiple fields (author, title, keyword, subject, etc) with one search and may offer additional ways to expand or limit your search.
If your first search strategy does not work, try another approach. Check out the "Help" or "Search Tips" to learn some of the search features specific to that database. Most databases provide similar features, but the methods may vary. Some common tricks:
Remember that you can also get help from the librarian.