I use cloudflare, W3 Supercache, audit images displayed and change sizes served on page load as it should be.
Run images through an optimizer, periodically I'll do this in bulk.
I combine all css into one file with sass and the similiar with js.
Depending on what plugins are installed on the site/theme, I may include core wp stuff in this knowing wp core updates require an update to those files as well.
Additionally and where possible, I will use css instead of javascript to help with perceived page speed.
Any cdn assets (not mine) I have I'll pull those so they are local to server. I do this with google fonts for instance. I currently have to do my dev work offline, so this helps prevent the site hanging up on trying to load pages it cant... and I still get my fonts
Without touching on things like redis and other more advanced back end tech, I think answers in this thread pretty much cover everything needed.
Perhaps code optimizations on theme templates and js as well... some of em are pretty bad hehe.