On the Internet, you are what you write. People have expressed this sentiment in various ways.
Like many catchy maxims this one also oversimplifies. But, ignoring photos, videos, and other multimedia, the reality is that we still communicate on the web largely with the written word. How you create those words determines others' opinions of you.
The Internet has changed how we write, introducing new words and new ways of putting pieces of writing together. But the fundamental principles of written communication still apply. In a nutshell, in the vast majority of cases you want to aim primarily for two things: clarity and interest.
In academic writing, people often try to show how intelligent they are. In business writing, it's how many buzzwords you know. And in Internet writing, the object is often to demonstrate how cool you are by typing and by using abbreviations and acronyms that let you move as fast as possible.
"PMFJI, but AFAIK his blog is SFW."
Too often, as with the above, such conventions can compromise clarity. Spelling out "Pardon me for jumping in, but as far as I know his blog is safe for work" takes longer but communicates better. The exception to this general rules occurs when you're sure everyone reading knows whatever acronyms, jargon, or slang you're using.
But people on the Internet do have short attentions spans, with a multitude of other blogs, sites, and other options to lure them away from your words. What's more, many people don't scroll down. What's not on the first screen won't be seen or read.
So get to the point quickly.
On the web it's often recommended that you use the inverted pyramid style of traditional newspaper journalism. Instead of a long introduction that sets the mood, lead with your most important point then taper down with less and less important points so that if readers stop reading, anything not read won't be missed as much.
One of the many magical things about the web is that even though it demands conciseness, it also allows for as much comprehensiveness as you like and your readers have time for. Web surfers may be in a hurry, but if they like what they see they'll want as much of it as they can get. The web facilitates depth by having fewer space restrictions than any other medium.
You should let readers know from the beginning what's available. Communicate your site's organizational structure by providing navigational buttons to the major sections at the edge of all or most pages, whether on top, bottom, left, or right.
Some sites also provide a site map or index that displays all the interior links for those who feel a need to get their bearings.
Links are fundamental to the web, but subdividing pages too much and forcing readers to tunnel down through too many links will also frustrate them. So there's a trade-off here, and it's often tough deciding whether to prevent overburdening readers with too much information per page or to prevent overburdening them with too many links per section.
One trick with long text passages that are best read from beginning to end is to include summaries. Readers interested in more detail can then jump to the longer passage. This is the same in principle to including a thumbnail version of a larger photo or a description of a video.
A second trick with long, multi-screen passages of text is to provide a printer-friendly version, stripped of images and other design elements. Some people will prefer to print out pages and read that way.
The web is a personal medium, and people expect real personalities and distinct voices. Infuse your individual or organizational personality into your text. Keep it conversational by using the personal pronouns I, we, and you.
Regarding the writing, use the KISS principle (Keep It Simple, Stupid). Write words, sentences, and paragraphs that are short and easy to digest. Indicate in context the meaning of terms that readers might be unfamiliar with. Avoid repetition and other excess verbiage. Use informational, not cutesy, headlines and subheads.
If conciseness combined with comprehensiveness is what most distinguishes web writing from other writing, interactivity is what most distinguishes the Internet from other media.
Build in ways for readers to react to what you write, to you and among themselves. Examples include feedback through email or web forms, discussion boards, and chat capabilities. When you do receive feedback from readers, be sure to acknowledge it.