It's easiest to learn by example. Check out some of these detailed walkthroughs.
How Changing Ad Networks Made My Site 8x Faster
This is a story about how I made a simple (stupid) choice to switch ad networks to increase ad revenue by a few percent. Yet it ignorantly turned a <2 second load time into an average of 15 seconds.
Optimizing Images for Web: A Practical Guide
Richard Lazazzera walks you through optimizing images on your site, average improvement of 30%
Improving Web Performance to Mirror Engine Speed
Great case study about how Algolia search optimized their site from 2.4 MB down to 700 KB
Reach out to me (see contact info in footer) to let me know of other examples
Feedback? Contact me: shane at httpfast dot com