Whether you’re planning to self-publish, query agents or publishers, or simply send your manuscript out for copyediting, following the guidelines suggested by Carol Saller of The Chicago Manual of Style for formatting your manuscript for submission will always be the safest bet.
Briefly, that means using Times New Roman 12pt, one-inch margins, double spacing, a half-inch indent at the start of every paragraph, and a ragged right margin instead of full justification. For chapter headings, insert either a page break or a blank line or two, center the chapter title (or number) and use headline capitalization, and don’t add a blank line below the heading. Begin the first line of the first paragraph of a chapter or section flush left (no indent).
For much more, see Ms. Saller’s post here:
And one more thing: Although it isn’t in the excellent linked article, per Chicago, when you’d like to mark a break in your storyline, give a visual cue that’s easy to see. Either use asterisks (I recommend three, centered) or some type of ornament, or start the (unindented) next paragraph with small caps. I’ve seen plenty of manuscripts that use only a single blank line, but those could be inadvertent hard returns, or they may come at the bottom of a page and be easily missed.
On behalf of your future agent, publisher, formatter, or copy editor–maybe me!–I thank you!