Find a body of text which is not preceded by text in a heading style. 2) Add a line of text between sections and use the ...

1) Find a body of text which is not preceded by text in a heading style.
2) Add a line of text between sections and use the Quick Styles gallery on the Home tab to select a heading style.
3) Click on the Outline Button on the Status Bar to see your document's overall heading structure.

Make sure you have at least one heading every two pages or so, and that your headings are 'organized' correctly (Heading 2 under Heading 1, etc...).