I really don't like using the word "breaks" in this context. You don't really break from one paragraph to another, you transition. Just as one sentence within a paragraph should logically and smoothly follow the sentence before it, the first sentence of a new paragrapg should logically and smoothly follow the last sentence of the previous paragraph.
Just as a single paragraph is made up of one subject, one idea, one topic, each scene is also a single subject, idea, or topic, so the paragraphs making up that scene have to be a continuous flow of the story the overall scene is telling.
Paragraphs are about clarity. The indent tells the reader something has changed, such as a character speaking, or or that that this character has finished speaking, and another character is going to speak.
A narrative paragraph indent tells the reader that one idea or bit of information has been stated, and that something new is being added to it.
Anyway, don't think about "effective breaks", think about "smooth transitions". If you write a single paragraph correctly, and end it when it should end, the first sentence of the next paragraph is what you would have written had you not changed paragraphs.
One exercise I learned in college was to write several pages of prose, we had to write five pages in that class, without even thinking about narrative paragraphs. Just tell your story without changing paragraphs.
When finished, go through and change paragraphs just by finding the point where it looks right and indenting.
You may well be surprised by how well you write in paragraph style when you aren't thinking about it.
