TIP #1: SEED ARTICLE
Begin your research with a "seed article" - an article that strongly supports your research topic. Then use a citation database to follow the studies published by finding articles which have cited that article, either because they support it or because they disagree with it.
TIP #2: SNOWBALLING
Snowballing is the process where researchers will begin with a select number of articles they have identified relevant/strongly supports their topic and then search each articles' references reviewing the studies cited to determine if they are relevant to your research.
BONUS POINTS: This process also helps identify key highly cited authors within a topic to help establish the "experts" in the field.
Literature Reviews: An Overview for Graduate Students by North Carolina State University Libraries
This video from the CEBM demonstrates how to use PICO to formulate a clinical question.