For me,
Minified or Gzip your CSS and Javascript files.
Don't use too much animation. For example, CSS3 Animation or Scroll Reveal
If you are encouraged to apply the 2nd point, especially for the scroll reveal, use a preloader. Scroll reveal won't work beautifully when your website is loading the assets as users will scroll down along your website before all the assets are loaded.
Don't use too much images. I recommend you to use images that are only important and relevant to your website.
If you can't fulfill the 3rd point, then reduce your images size as much as possible without losing the quality of the images. Most of high quality images on the internet has huge size (i.e. 5MB). However, if the size reducing affects the image quality but you feel that the image is good enough to look, then go with it. This tricks works well for me.
Ensure that you use all classes in your CSS files. If there are classes you didn't use, eliminate them. This point comes out a lot when you use a CSS framework. CSS framework contains many sets of classes that you probably won't use all of them. CSS framework like Bootstrap offers you to customize what components do you want to use on your website.
Good Luck :)