Did your search return too many or too few relevant results? Here are some strategies that may help. 

Too Many Search Results

Finding the right search terms or keywords. Try changing the keywords or terms. Brainstorming keywords will be helpful for this. Think of terms that are more specific. 

Using too few search terms. Each time you put in another search term, you will retrieve fewer results. Start with a small number of keywords and then add more terms or try different terms based on your results.

Not using limiters. Limiters such as date and resource type retrieve a targeted, results list. Do you need to only use scholarly peer-reviewed articles? Should your sources be fairly recent? In each database, look for the limiters that meet your criteria for your research.

Notice the default search options. By default, most databases search in the title, author field, abstract, and subject terms associated with the article. Experiment with searching in just the title or subject field in order to get more targeted results.

A topic that is too broad. Think about a more focused aspect of your topic or various angles of your topic.  If you are looking at gay soldiers in the US military, then examine changing attitudes towards sexuality, military culture, arguments against or for gay soldiers in combat units.

Too Few Search Results

Try a database on your topic. Search in a database that specializes in a certain subject. If you need a subject-specific database suggestion, try the Databases by Subject page or databases recommended in one of the library's Research Guides. Be flexible and persistent, you may have to try several different databases.

Brainstorm search terms. Try changing up the terms you use in your search. Brainstorming keywords will be helpful for this. Sometimes by just using a different term that essentially means the same thing, you will get a very different results list. Wikipedia isn't a good source to use for your paper, but it can be an excellent aid in brainstorming search terms. 

Using too many search terms. Each time you put in another search term you will get fewer results. Start with a small number of keywords and then add more terms or try different terms based on your results.

Using too many limiters. Limiters such as date and resource type give you a more targeted results list, but sometimes you can use so many that you end up with zero results. Try using only those that are absolutely necessary. For instance, if your professor requires only scholarly peer-reviewed articles, limiting to peer-reviewed articles would be essential.

A topic is too narrow. You may need to think more broadly about your topic. For example, if you are researching the impact of "Basque terrorism" and a specific town in Spain, you might broaden your search to ljust look at "Basque terrorism." Also, you may need to break your topic into different parts and search them separately (the Basque separatist movement then the demographics of the Spanish town), then synthesize the information.