While writing, I usually read aloud the text: I like that what I write be not very different from what I would say. Since paragraphs are separated by pauses, which are usually quite obvious when talking, a bad paragraph break or a missing one tends to make itself quite obvious in this way.
This does not constitute a rule, of course, for paragraph breaking, but is a useful way to probe them.
Good paragraph breaking is like pornography, in a way.