PICO is a useful tool that can help you define the question's core concepts.
There are four components that typically make up a clinical question:
A typical database search filter allows you to narrow results so that you retrieve articles that are most relevant to your research question. Filter types vary by database & include:
In a systematic review search, you should use care when applying filters, as you may lose articles inadvertently. For more information, see Cochrane Handbook for Systematic Reviews of Interventions 2019
These are published and tested filters to help you refine your search when databases don't include them
For more helpful information, see Search Filters - Overview from the University of South Australia
Yale University's Harvey Cushing/John Hay Whitney Medical Library has an excellent set of video tutorials that will walk you through the steps of searching the literature for a systematic review.
"This series of tutorials covers the fundamental concepts and general procedure of searching the health science literature in a systematic manner. They will mainly focus on systematic searches required by a "systematic review." The goal of these tutorials is to ensure that your search is comprehensive, methodical, transparent and reproducible, so that your conclusions are as unbiased and close to truth as possible."