Better WordPress Minify
Allows you to combine and minify your CSS and JS files to improve page load time. This plugin uses the PHP library Minify and relies on WordPress’s enqueueing system rather than the output buffer, which respects the order of CSS and JS files as well as their dependencies. BWP Minify is very customizable and easy to use.
Useful resources to help you get started and make the most out of BWP Minify