Get Your Headings in Order
The heading structure of your content is used both for navigation and also to understand the relationships within your content; i.e. whether things have equal importance, or if items are subordinate to other items. When you are creating headings in your content, click on the "Normal" drop-down item in the rich text editor. Then choose the appropriate heading level for your text.
Remember that your heading structure should be similar to an essay outline. Headings should descend numerically when following the natural numbering order, i.e. a heading level 2 follows a heading level 1. You shouldn't skip numerical order, from a level 1 to a level 3, however you can jump back up to a higher level.
A recent Ohio University Compass magazine article provide more detail on structuring your content with headings.