What are beats? Beats are bits of action narrated during dialogue. This would be called stage business or blocking when reading a stage play. There are also internal beats where a character has a short passage of interior monologue. Beats can help change the pace and tension of a scene depending on how many are used. Fewer beats give a faster pace and can help build tension in an argument scene. Too many beats can stop the pace of the story and move at the same speed as an entire page of narrative summary.
Don’t use too many beats and don’t use too few. What’s the right amount? It depends on the scene. Use fewer beats to build tension. Use more beats to slow things down and give the reader some time to breath. Peaks and valleys. In most cases, there only needs to be enough to keep the reader in the scene. If the scene takes place in a machine shop, an occasional commentary on noise being heard will remind the reader where the characters are speaking. Beats are also important for showing body language to the reader. This is as important as what the character says.
Beats help break up the page making it more engaging. A full page of a one paragraph narrative summary may look boring on the page. That narrative may be important but it’s easy to break it up with beats or internal beats. Through a couple internal beats into the paragraph and now there’s several paragraph on one page and some short internal monologue. But don’t overdo it. If it isn’t important to the story or plot and doesn’t help move the story or plot along its path, it isn’t needed. Do what’s right for the scene and the story overall.
The best place to learn how to improve one’s writing is with Renni Browne and Dave King’s “Self-Editing for Fiction Writers: How to Edit Yourself into Print.” If I were teaching a class on fiction writing, this is the book I would use as the course textbook.