Test whether your question is likely to lead to an ample research paper with a fast search at the library site. You’ll need enough ideas, opinions, facts, statistics, and expert testimony to address your question. If you turn up a skimpy list, change search terms. For hundreds of sources, refine your question. Aim for a question that is the focus of a dozen or twenty available sources. If you need help, talk to a reference librarian.
Also decide which types of sources to target. Some questions require a wide range, others a narrower range, restricted by date or discipline.
To review the types of evidence, see pp. 44–45.