Before embarking on your systematic search, you'll want to define your research topic in an easily searchable way. This involves separating out the key concepts of your research question. There are various tools to help you do this. One commonly used in health systematic reviews is PICO; for scoping reviews, PCC:
The worksheet and slides below can help you formulate a searchable question.
You'll want to check whether there already is a recent, well-done systematic or scoping review on your topic, or if another team has registered a protocol indicating a review is underway. Search the databases below, or others in your subject area or Google Scholar, to find reviews or protocols.
It is also a good idea to do some basic, exploratory searching in a database in your field to gauge how much literature there is on your research question, and what inclusion and exclusion criteria might make sense to answer it. Based on the number of results, you may opt to broaden or narrow your research question.
For ideas for databases in your field, consult a Research Guide or a Subject Librarian.