Use built-in heading styles
If you have sections of content with a section heading for each section, you should always use proper heading styles for those section headings. For example, let’s say you have a training guide that has three sections – Searching for items, making a purchase, and reviewing a purchase, those three sections would be assigned as heading 2s. The title of the document, email, or webpage is always the heading 1. Any sub-sections under each heading 2 would be a heading 3.
Always keep to the heading hierarchy
You should never skip a heading level. If you have a heading 2 and decide to have a couple sub-sections under that heading level 2, those sub-sections should be heading level 3s, not heading level 4s.
If you have no sections, no headings are needed
Sometimes you are writing either a one section webpage, one page document without sections, or a short email without sections. In this case, no headings are needed.