From the definitive text of Robert Bringhurst’s The Elements of Typographic Style, 4th edition.
“The function of a paragraph indent is to mark a pause, setting the paragraph apart from what precedes it. If a paragraph is preceded by a title or subhead, the indent is superfluous and can therefore be omitted.”
In other words, if your paragraph has a heading, don’t indent the paragraph. Subsequent paragraphs can have an indent. I also use line spaces instead of indents as a style choice.