A systematic review needs to have a preplanned protocol (a document of your specific methods).
The protocol should clearly explain any changes that are made to the review method later on. This way, the review method is reproducible and the results are objective and trustworthy.
Ideally, the protocol and any changes should be documented publicly before the systematic review itself has been completed. This will alert other researchers about your work in progress so that the same review is not repeated by others.
The review should also be systematically and transparently reported, so that there is minimal reporting bias. Potential biases should also be identified.
Before writing a review protocol, it is a good idea to prepare a brief synopsis (a bullet-point overview) that lists your contributors, aims, and strategies.
The synopsis can be used as a guide for developing the protocol into several other items: