Start with structure
Clean URLs, a logical page hierarchy and useful internal links help both users and search engines. SEO becomes much harder when it is expected to repair a confusing architecture after launch.
Canonical, hreflang and indexability
Every indexable page should point to the correct canonical URL. On multilingual sites, hreflang should connect equivalent language versions rather than simply pointing to homepages. Robots directives, redirects and staging URLs also need review before launch.
Metadata and structured data
Titles and descriptions should accurately reflect content and be unique where appropriate. Structured data such as Organization, BreadcrumbList, Article or Product can help search engines understand a page when used correctly and without unnecessary markup.
Performance and mobile
A website that loads slowly or constantly shifts its layout creates a poor experience regardless of SEO. Correct image sizing, sensible JavaScript, caching and responsive layouts are part of the technical quality of the project.
A launch checklist should treat SEO, performance and UX as one system rather than three unrelated tasks.