Title tags are used to establish hierarchy of content, and inform search engines about the topics on the page.
Using title tags properly can influence your SEO, and improve your page ranking in search engines.
Use title tags in a chronological order
Always use title tags in a chronological order. H1 comes before h2, h2 comes before h3, and so on.
Title tags help determine the information hierarchy. H3 is a sub-category of H2, and H4 is a sub-category of H3. H4 does not occur if an h3 has not happened.
Common title tag misuses
Using titles for their style
A common misuse of title tags is to use them for styling text. You aren’t supposed to use title tags based on their appearance. Instead, use title tags with the correct hierarchy usage, and style the title tags to fit your aesthetics.
More than on H1 tag
Using too many H1 tags is usually incorrect. Use only one H1 tag per page or section, depending upon if your doctype is HTML4, XHTML, or HTML5.