Heads:

Make the topmost head on the page an H1, worded so that the user knows why the page is important.

Make sure that heads clearly indicate the content of the sections.

Avoid in-line character formatting to heads--the results are unpredictable, varying from browser to browser.

Organize your text so that the hierarchy is no deeper than four levels. Lower-level heads are hard to distinguish and disorienting to online readers.

Lists:

You can include a greater number of lists on a web page than on a printed paper page.

Use numbered lists when the order of entries is important.

Use unnumbered lists whenever the sequence of the entries is not important.

Limit the number of items in a single list to no more than nine.

Generally, limit lists to no more than two levels: primary and secondary.

Captions:

Make sure that the caption uniquely identifies the illustration or table. For example, do not give the same name to the caption as you have given to a head on the same page or another page.

Caption illustrations except when the context is so clear that captions would be redundant.

Don't number illustrations sequentially by chapter, section, or the like. If a screen capture has more than one illustration to which you must refer, use a simple numbering scheme (Figure 1, Figure 2). If you follow the "one topic per screen" guideline, however, figure numbers usually won't be necessary.

Don't include figure captions unless you need them or have a lot of conceptual or reference material.

Hyperlinks:

Don't use a hypertext link if the information can be succinctly presented on the current page.

Don't mention that you are providing links at all.

Use a description of the information to be found in the link, or perhaps the link address.

Use hyperlinks to provide supplemental information like definitions of terms and abbreviations, reference information, and background reading.

Cluster cross-references under a "See also" (or similar) heading where appropriate. Generally, such lists of cross-references are easiest to read if they include only headings or titles with a few words of explanation.
NOTE: The left navigation bar on www.sun.com correctly lists cross-references with no explanatory text.