Read the report
Run Lighthouse on a production-like preview. Note which metric fails and which element is named for LCP.
LCP
Compress the hero, set width/height, and use modern formats. Avoid late-loading carousels as the largest element.
CLS
Reserve space for images, embeds, and banners. Load fonts without layout thrash.
Third parties
Audit tag managers. Defer non-critical scripts. Cap marketing pixels on landing templates when budgets are tight.
Full guide: Improve Core Web Vitals before launch.