A new site doesn't need a fully mature SEO program on day one — it needs a short list of foundational items done correctly before anything else is worth pursuing.
Confirm the Site Can Actually Be Crawled and Indexed
Nothing else matters if search engines can't discover and index your pages in the first place, so this comes before any other optimization.
Get Titles and Descriptions in Place on Every Page
Even a simple, accurate title and description on each page beats a technically perfect site with blank or default metadata.
Submit a Sitemap and Set Up Basic Tracking
A sitemap and a connected analytics or search console account give you the visibility to know whether your early efforts are working at all.
Next step: Use the SEO Audit to confirm your new site's foundation is solid before you move on to anything more advanced.