Most on-page SEO work is really about making sure a handful of specific, checkable things are actually correct — a page has one clear H1, its meta description is within Google's display length, its images have meaningful alt text, and its social preview looks right before anyone shares the link. None of this is complicated individually, but it's tedious to verify by hand across a whole site.
A meta description doesn't directly affect search rankings — Google has been clear about that — but it strongly affects click-through rate once a page is already showing in results, since it's the preview text a searcher actually reads before deciding whether to click. A vague or truncated description genuinely costs clicks even when the page itself ranks well.
Heading structure (H1 through H6) matters for two different audiences at once: it helps search engines understand a page's content hierarchy, and it helps screen reader users navigate a page efficiently, since screen readers can jump between headings the same way a sighted user visually scans them. A page with a messy or skipped heading structure — an H1 followed directly by an H4, for instance — makes both jobs harder.