Q. I have four different levels of headers. What should be the format (font, bold vs. italic, centered, etc.)? Thanks for your help!
A. The convention is for the copyeditor not to style the headings but merely to label them (a, b, etc.) so the designer or typesetter can impose the specified stylings, whatever they are. If you are writing a paper not for publication, however, you might follow the suggestions in the paper-formatting appendix to Kate Turabian’s Manual for Writers of Research Papers, Theses, and Dissertations: “Each level of subhead should be consistent and different from all other levels, and higher-level subheads should be more visually prominent than lower-level ones” (10th ed., § A.3.2.4).
Turabian’s caveat about subheadings is also worth considering: “Unless you are writing a very long and complex paper, think carefully before using more than two or three levels of subheads. Rather than being helpful, they can become distracting. You should have at least two subheads at any level within a chapter; if you do not, your divisions might not be logically structured” (§ A.3.2.4).