Start with optimized images. Resize pictures to the dimensions they will actually be displayed at and consider modern formats such as WebP or AVIF.
Choose good hosting, turn on HTTPS and make sure server-side caching is set up appropriately for your site.
Avoid installing a plugin for every tiny feature. Each plugin has a different performance profile, so audit what you use.
Use browser and page caching carefully, especially around checkout, login and other dynamic pages.
Test real pages regularly. Core Web Vitals are useful signals, but improve the actual visitor journey rather than chasing a perfect score.