Conceptual h1 |h1|

Leap straight into the introduction. Don't include a second heading after the topic heading. In the introduction

Explain the concept that underlies the topic. This often involves using boilerplate wording and key phrases that get repeated throughout a section devoted to a single concept. Try not to quote other topics verbatim, but worry more about consistency than originality.

Outline the facets of the concept the topic covers. Do this in the order they occur in the topic.

Heading 1 |h2|

When creating the heading:

Include a specific verb indicating what you’ll learn from this topic, such as adding, creating, handling, and returning.
Make the heading specific enough that the reader can scan to it and know as precisely as possible what he or she will get from it.
Double check that the order of headings (and therefore of sections) is justifiable. That is, make sure there’s a reason that one section comes before another. In many cases, information in one section is necessary to understand the concept in another section, so arrange the sections accordingly. If all of the sections are equally important and no section contains information important to another, it may be worthwhile to reconsider why they all coexist in the same topic.

The following guidelines are a general roadmap for crafting a section. These are not hard-and-fast rules, but rather are designed to get you going.

Introduce—briefly—what you’re talking about.
Explain why you need to know it. This is the one that gets left out most frequently. In reference topics this information is assumed. In conceptual topics it shouldn’t be.
You needn’t be lengthy with this information. A sentence is often plenty.
Include practical information about applying the information. In other words, tell them how to use what you’ve introduced. In topics that just introduce the concepts without telling you how to use them, include a link to the section that explains how to use the concept.

There are exceptions in terms of length and importance, of course, but each section should be able to answer the what, why, and how questions.

Heading 2 |h3|

For second- or third-level headings:

Make sure each relates obviously to its superior heading. More often than main headings, these make sense without a verb set-up. But if possible, keep the verbs comin’.
Again, keep the order justifiable.

Because second- and third-tier sections are subordinate to sections that explain a concept thoroughly, they allow you to assume slightly more about what the user already knows. So you can be more frugal with the what and the why parts. This doesn’t mean you can skip ‘em necessarily, it just means you can assume more. Otherwise, the same guidelines apply to these as to the first-level sections.