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 View tab and click the Navigation Pane checkbox to see a list of 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...).