Most of us are used to doing most of our writing for scholarly articles, brochures, newsletters, and the like; that is, we write for print. Readers of the printed word generally read sequentially, from start to finish, in a linear fashion, and we write linearly to accommodate them.
On the Web, users rarely read this way. Instead, they scan the page for the information they want, and if they do not find it quickly, they leave. Web readers focus on headlines, keywords, and brief summaries, and do not follow a linear pattern (reading the whole page from top to bottom). Instead, they start from the center of the screen, look left and right, and then jump around, skipping long passages and following links in a random pattern.
It is important to also keep in mind that reading on the Web is physically different than reading print. Desktop, laptop, and tablet users are positioned differently. Reading from a monitor is 25% slower than reading print, and can cause eyestrain. Users with visual disabilities have an even harder time, as screen readers and magnifiers can make reading very slow and tedious.
We use the United States government's Plain Language guidelines to govern our writing and keep it concise, conversational, and scannable without "dumbing it down."
Passive voice writing is boring, and does not indicate to the reader that whatever they're reading about is something they can do, get, or become. Third-person language reads as stilted and can be awkward.
Try not to use language that builds in the need to revisit and update your words. If you are referring to content that does not yet exist - for example, plans that you have to add a piece of information "later" - simply omit that reference. "Later" is vague, and often never comes.
Web readers scan text rather than reading it as they might on paper.
Use no more than half of the words you might use in print. If you can cut a word, cut it.
Express one thought at a time and express it only once; avoid redundancy.
Don't add content for the sake of adding content - get to the point, then stop.
Use keywords to improve scannability. Use these keywords as links. (And avoid "click here" - don't give directions, take them where they need to go!)
Use bulleted and numbered lists to break up information into scannable chunks.
Keep headlines short, and use brief but meaningful subheadings. Don't use links in headlines.
For most grammatical and style considerations, including numbers, dates, and times, follow the Associated Press stylebook.
Put your conclusions and most important info at the top of the page, with details further down. Avoid introductions and "welcomes" - just get to the point.