Double space the entire paper for APA (with no extra line spaces)
Under “Paragraph” choose double space, and also check the small box that says: "Don’t add space between paragraphs of the same style.”
Some basics for APA set-up (also in video and in the Publication Manual of the American Psychological Association, Chapter 2: Manuscript Structure and Content (pp. 21-59):
Also - Review the video below for more details on these common rules, running head and other APA issues.