Sustaining a reader's interest isn't just about using proper grammar. The best pieces tend to be broken into clear structural components using what are known as "subheads." Much as a paragraph is used to contain and express a specific idea, a subhead can be thought of as a way to contain and express a much larger concept. In some cases, subheads help to reinforce the message of the paragraphs that they precede; in other cases, subheads are used as a kind of road-map for a longer piece.

Imagine an essay that describes the results of experiments conducted with a spectrograph. The writer composes a 9-paragraph piece that describes his initial hypotheses, his research results, and his interpretation of those results. After he finishes writing the essay, he realizes that each section is a kind of mini-essay in of itself. He decides to insert three subheads to help guide his reader through the piece:

Subhead 1: My Initial Hypothesis?
Subhead 2: The Spectrograph Results?
Subhead 3: How the Results Influenced My Research

Readers that come across these subheads will be able to instantly determine what the essay is about. They will also understand which section correlates to what subhead, allowing them to skip forward to the section which is most germane to their interest.

In this manner, subheads are very similar to chapter headings. They allow the writer to naturally break up the piece into digestible sections. This is especially helpful should the reader become distracted while reading the piece. Subheads allow readers to quickly jump in where they left off without having to re-read the entire piece.

This clear structure also benefits the writer. By inserting subheads, writers will be able to more readily identify tangents, redundancies or misplaced sections in their work. This allows writers to easily craft an elegantly organized piece.

Some writers enjoy using subheads for "shock value." They will insert slang terms, epithets, or use visually provocative techniques such as all caps or a slew of symbols. These techniques are rarely appropriate for carefully crafted pieces. While the occasional jolting subhead can be amusing, in general writers should steer clear of all these techniques if they wish to keep their readers engaged.

Subheads, unlike sentences, should be used sparingly. A piece that is peppered with subheads may actually become more, and not less, difficult to read. Although there is no hard and fast rule, each subhead should serve as a clear header for a section that contains at least two to three paragraphs. A subhead per paragraph can induce reader fatigue.

Grammatically, it should be noted that while the use of fragments is frowned upon in all other forms of written English, subheads can consist of a fragment as long as they capture the intent of the section. They can also take the form of declarative or interrogative statements. Regardless of which form is used, writers should always read their subheads aloud to make sure they are appropriate.