Most “speed up WordPress” lists give you 30 tips in random order: enable GZIP, limit revisions, disable hotlinking. Some of those save milliseconds. Others save seconds. If you do them in the wrong order, you spend a weekend tweaking, and your PageSpeed score barely moves.
This improve WordPress speed guide is ordered by impact. Measure first, then fix the big things (hosting, caching, images), then the medium ones (scripts, fonts, plugins), then the small housekeeping. Stop when your site is fast enough.