Start with the two that matter most
Enable full-page caching at the server level, then move the site to the newest supported PHP version. On our test install those two changes alone took largest contentful paint from 2.4s to 1.3s.
Everything after this point is refinement. Do not reorder the list.
The remaining six steps
Work down in order, measuring after each change so you know what actually helped.
- Convert images to WebP or AVIF and set explicit width and height attributes.
- Clean the database: post revisions, expired transients and orphaned metadata.
- Audit plugins - deactivate anything not used in the last 90 days, then delete it.
- Put a CDN in front of static assets so images and CSS are served near the visitor.
- Defer non-critical JavaScript and drop render-blocking third-party scripts above the fold.
- Switch to a lightweight theme if the current one loads a page builder on every request.
How to measure honestly
Test the same URL, logged out, three times in a row and take the median. Test once from a location far from your server too - a single number from one nearby test tells you almost nothing about real visitors.
Field data beats lab data. If you have real-user metrics available, trust those over any synthetic score.
Takeaway: Do caching and PHP version first - together they were worth more than the other six combined.