The protocol is a published plan that describes the objectives and methods you will follow for your review.
Before you write your protocol and to ensure the uniqueness of your review, you should search the registers of completed and ongoing studies. Below, are some suggested starting-points for your searches.
When designing your protocol, refer to the reporting guidance for your type of review, to ensure that you do not forgot to include something in the initial stages that you are expected to report at the end. The following resources may also be of help:
It is recommended that you add your final protocol to a register to raise awareness among researchers. PROSPERO is just one register you might want to consider:
The Library of the University of Melbourne provides a helpful infographic about common inclusion or exclusion criteria.
Module 2 in Cochrane Interactive Learning provides advice about the key components and structure of a protocol. The Library is subscribing to Cochrane Interactive Learning.