The literature search element of a systematic review is the next step after you’ve created a well-defined question that the systematic review itself is trying to answer.
Best-practice is to perform your literature search across at least three separate databases. The two most common are Embase and MEDLINE, with the third (and fourth and fifth!) varying depending on the subject area of your systematic review. Additional databases can include sources of grey literature like ClinicalTrials.gov or databases of systematic reviews such as Cochrane (with a lot of Cochrane content being available in both Embase and MEDLINE).
Your literature search needs to use a well-constructed and thorough search strategy. Following a framework like PICO (Problem, Intervention, Comparison, Outcome) or SPIDER (Sample, Phenomenon of Interest, Design, Evaluation, Research type) can help you ensure you’re not missing anything. It can also help to use a database search platform that allows you to save and edit your searches. This can make it easier to demonstrate your search strategy is truly reproducible and exhaustive.
Your search strategy will also benefit from using Embase and MEDLINE’s thesauri to refine your search keywords. Using medical synonyms (like those built into Dialog) can also be helpful, both for saving your time and ensuring you’re not missing out on any common synonyms for your search terms.
And as a final point, make sure you’re able to refine your results consistently across all the databases you’re using. This is easier if you’re using a single platform to search multiple databases as you can limit date ranges, publications, author, etc. with a single click, rather than trying to do this consistently across individual databases.