There are many wordpress plugins that can help boost site performance. Here is a list of plugins recommended by AspieSoft.
- WP Super Cache
- Native Lazyload
- Flying Images by WP Speed Matters
- Flying Fonts by WP Speed Matters
- Flying Pages by WP Speed Matters
While Caching and Compression can help improve performance, if your website has been running for a while, or you often experiment with different plugins, it can help to clean up any options or settings those plugins leave behind. WordPress usually autoloads and preloads plugin options to improve performance, but loading unneeded settings can slow down your site drastically. Here are some database cleaning plugins you can use to improve performance of an old website.
(Note: these plugins can modify the database, use at your own risk)