First and foremost if you want a fast website stop using WordPress or any other CMS that uses a database to serve your pages. Your best option is to serve static HTML that can be compressed and cached. You can use WordPress as a true CMS that outputs static content to your public web directory. Have a look at Grav as a CMS alternative.
Then as others have mentioned you can perform optimization to your web pages by optimizing images served, concat JS/CSS, loading critical styles and JS in the head and every else before the body close, lazy loading images, using a CDN, caching resources...