Found a neat little build in feature where you can check your images against known composition rules while cropping.
You can use it to learn and master your compositions, and at times tun a great image into a really great photograph.
It's quite simple and dosen't require any plugin.
In develop module select any image hit R to open crop tool by default this overlays the Rules of third composition rule. now press O to shuffle between the 5 know rule sets.
In order from lightroom
Remember that the rules are only a guide to help you crop into a pleasing composition for your viewers. There is nothing wrong in breaking and bending the rules of photography to your liking.