Load speed has a small effect on search rank itself. But a slow website leads to a high bounce rate which leads to lower search rank. The main reason sites load slowly is that images are not compressed properly. Make sure they are web resolution, 72 dpi and no larger than you need. If you are on WordPress you can use a compression plugin like WP Smush or Imagify to compress them further.
Another thing you can do is make sure the site is cached. Caching delivers a static version of the site to reduce load speed. Using a caching plugin with a Content Delivery Network like Cloudflare can really speed up your load time. Some advanced techniques involve Gzip compression and removing query strings. Use a tool such as GTMetrix or Pingdom Speed Test to see what your speed is and their suggestions to speed it up.
Contributors: Gabriel Bertolo from Radiant Elephant