Audio/Video/Image Best Practices

Hello, I find that many students and other users don’t really have any knowledge of best practices (and embedding options) when using audio/video/images on their websites. I see lots of people uploading 4000x4000 images when they are just used at 300x300 and full HD videos for little clips in a tiny window. Of course this eats up the quota quickly and degrades website performance.

There are guides online for this but most of them are either outdated, covered in ads or are sites pushing people to use a particular online software application. Is anyone aware of a guide created by a university or non-profit (maybe by Reclaim institution?) that covers this well? I’m trying to see if something is already out there before I re-invent the wheel.