If this is a site under development, versus a retired page of content, confirm it is an HTML5 page, using the HTML5 doctype: <!DOCTYPE html>
This is an important and loaded checklist item. If the site is HTML5 (first line is <!DOCTYPE html>), tags like <header>, <footer> and <nav> should be used. Menu items should be marked up as an ordered list.
Common things that should be avoided are using the <br> tag for formatting, using <b> when you mean <strong>, or worse, using <b> when the content is a heading.