Once you have your inclusion and exclusion criteria, as well as the databases you intend to search, you can begin searching.
Make sure you keep a record of your search strategy so that your review is reproducible.
You will need a place to store the studies you find so that your reviewers can assess them.
There are also tools that have been created to assist in managing your search results when performing systematic reviews.
See the following article on how to find and remove duplicate studies when searching: Identifying and removing duplicate records from systematic review searches, by Yoojin Kwon, Michelle Lemieux, Jill McTavish, and Nadine Wathen.