Ask HN: What are the best resources to learn about performance marketing?

We're in the early stages of experimenting with performance marketing (PPC on Google, Facebook, Instagram etc.) and have been running a few small experiments.

Given we now have baseline figures for what ballpark CTR, CPC and CAC figures could be, we're now trying to figure out what the most effective levers are which we could use to optimise.

If anyone has any thoughts or go-to resources, I'd love to read them!