I’ve been working with WP Rocket’s support team for a number of years, so I’m not only intimately familiar with the plugin, but I’ve also seen a lot of mistakes that customers make when they attempt to use it.
Even though it’s one of the easiest WordPress caching plugins to use, speed optimization is inherently technical and complex. It’s common to get confused or overwhelmed when using optimization plugins.
But here you have the “ultimate” guide, from the horse’s mouth. Even if you don’t use WP Rocket specifically, many of the guidelines apply to caching plugins in general.