The best place to start in identifying keywords to search is by going back to your research question. The main concepts are usually good keywords to start out with. 

Example

How does the use of Open Educational Resources (OER) impact student achievement in a higher education setting?

Keywords: Open Educational Resources (OER), "student achievement," and "higher education."

Using your the keywords you identified, you generate a list of potential synonyms or related terms 

Example

(OER OR “open educational resource*”)
AND ("student efficacy" OR "student outcomes" OR “student achievement”)
AND (“higher education” OR college OR University)

Search tips

• Use Boolean operators AND, OR, and NOT to broaden and narrow your searches
• Group concepts with parenthesis
• Put phrases in quotation marks
• Use asterisks at the end of the root of words to search for all forms of the word

1. Search systematically: Write out keyword strings, search one database at a time, track of the number of results while refining searches. 

2. Adjust the search for each database if necessary: Different databases can use different terminology. 

3. Utilize the database thesaurus when possible to identify subject terms 

4. Save your searches: This is a good way to keep track of what you have searched and what the results were.

Your searches will often produce a lot of results, and not everything will be relevant to your specific research question. How do you know what to include?

1. Reading a journal article efficiently: Start with reading the title, abstract, methodology, and conclusion. This can help you decide if it should be saved to read later, or if it is outside of the scope of the research question.
2. Look at number of times an article has been cited: This is not the main determinant for whether an article should be included in your review, but highly cited articles can be an indicator of importance on the subject. Looking at references and times cited can also lead you to additional literature. 
3. Be careful of scope creep: When doing research, you will find a lot of interesting avenues related to your research. Make sure to stay within the scope of your research question, otherwise you risk incorporating too much for the size of the project, losing the focus, and including articles that don't quite fit the scope.
4. Always return to your research question: This can be helpful when trying to figure out if an article should be included and if you are encountering scope creep.