Choose a representative page
Start with a page that contains the elements visitors actually use. Inspect images, fonts, scripts and requests. Record the test conditions so later comparisons are meaningful.
Spend the budget deliberately
A large image, extra font or embedded tool should have a clear purpose. Resize assets for their use and avoid loading features before they are needed. Work on the measured bottleneck rather than applying every optimization you have heard of.
Check the experience after the change
Core Web Vitals cover loading, responsiveness and visual stability. Combine those measurements with direct checks of the task the page supports. A faster page still needs understandable content and working controls.