The title tag
Unique across the site, fifty to sixty characters, subject first and site name last. It is the main element shown in search results — and two pages sharing a title compete with each other.
The meta description
Under a hundred and sixty characters, or it is truncated. It does not affect ranking but decides the click: it should announce what the page answers, not describe the company.
Heading structure
One h1 per page, matching the subject. h2 for sections, h3 within them. No skipped levels. This hierarchy serves screen readers as much as search engines.
Images
An alt attribute describing function, not appearance. A modern format at an appropriate size: a 4000-pixel image displayed at 600 slows the page for nothing. And declared dimensions, so the layout does not jump on load.
Speed is not a comfort detail: it is a ranking factor, and above all the first cause of abandonment. A page taking more than three seconds loses a substantial share of visitors before being read.
Links
Link text that describes the destination — never "click here". Two or three contextual internal links to related pages. And a check that each resolves: a dead link in a menu costs more than a missing page.
The final check
Canonical URL declared, page present in the sitemap, and nothing in robots.txt blocking it. These three omissions are the most common, and any of them makes a good page invisible.
our piece on UX design sets out the other activities of the profession.