The protocol specifies the methods to be used in the review with the aim of minimizing bias and needs to be clearly stated. A well written protocol will include the following elements:
What types of studies will you include? What population do you want to include in your review (may include age, gender, nationality)?
What search terms will you use? Who will complete the search? On what date will the searches be run? What databases/sources will you use?
How will studies be selected for inclusion? How many people will review the studies? What are their qualifications?
How will data be extracted from selected studies? Who is performing the data extraction? What tools are they using?
How will the quality of included studies be assessed? What tools or criteria are being used?
How will the results be synthesized? Will a meta-analysis be performed on the data?
How will results be shared?
Consider registering your completed protocol in PROSPERO, an International Prospective Register of Systematic Reviews. PROSPERO is also a great place for you to find examples of existing protocols if you're not sure how to write your own.