In order to enhance the performance of your GeoServer, you may consider monitoring usage. Monitoring lets you know what the most used services and datasets are.
A low-level approach, and the simplest possible is to analyze the GeoServer logs and the web server logs. All requests are, in some way, tracked there, so it is just a matter of how to find a convenient way to extract and organize them in a structured data model.
Analyzing the logs may be quite challenging. Besides, according to the detail level, you may find too much information or totally miss the piece you are looking for.
Luckily, GeoServer developers have been working on a clever extension that helps you to analyze what requests GeoServer has been receiving. Unsurprisingly, it is called the Monitor Extension.