Before diving into searching the literature you must create a search strategy. Building a search strategy can be thought of as two different components, the search terms and the limiters. 

One of the best ways to brainstorm search terms is to use a technique called PICO. 

What is PICO? 

PICO is a strategy for going from a written research question to keywords you can use to search the database. 

P = Patient 

What patient group or problem are you looking at? Are you focusing on patients of a particular age or gender? 

I = Intervention

What is the intervention, exposure, or prognostic factor you are looking at? Keep in mind that the definition of intervention is broad. An intervention can be a drug or treatment, but it could also be the implementation of an educational program or training tool. 

C = Comparison 

Are you comparing the intervention with something? Are you comparing a drug against another drug or a placebo? 

O = Outcome 

What is the desired outcome? 

Example: 

Does drinking cranberry juice prevent urinary tract infections? 

P (Patient or problem) = Urinary tract infection 

I (intervention) = Cranberry Juice 

C (comparison) = No cranberry juice

O (outcome) = Prevention of urinary tract infections 

Example search string: "urinary tract infection" AND prevention AND "cranberry juice"

Don't fret if your research question cannot be mapped to PICO! You can still develop good search terms from a written sentence or question. 

The key to PICO is pulling the most important words out of your research question and reorganizing them with search operators. This basic concept can be applied to any research question, even if it doesn't fit the PICO framework. 

You can limit your search results!  You can limit by date (for example, to get more recent results).  Many people like to limit their database search results to peer-reviewed or scholarly only. These limiters tend to be available to the left of your search results.