Librarians can assist you in finding journals that are appropriate for your manuscript, but the following tools can also give you a head start by providing a list of suggested journals.
1) You'll need a descriptive, working title for your project / manuscript, even if it's not the final title.
2) Your manuscript abstract will also be handy, or at least a few sentences describing your project / manuscript. The more, the better. The more descriptive using keywords you've seen in other articles on your topic, the more relevant and precise the recommendations will be.
3) Common, descriptive keywords for your project / manuscript are helpful. Again, use keywords used in articles / topics similar to yours.