This guide from the Alliance for Useful Evidence is an introduction to systematic review and the necessary steps that should be considered as a part of the process.
It describes the logic of systematic reviews and mixed methods reviews and the main stages of undertaking a review.
Gough, D., Oliver, S. & Thomas, J. (2013). Learning from Research: Systematic Reviews for Informing Policy Decisions: A Quick Guide. A paper for the Alliance for Useful Evidence. London: Nesta. Retrieved from https://apo.org.au/node/71119