"People rarely read Web pages word by word; instead, they scan the page, picking out individual words and sentences." Jakob Nielsen
Writing for the web is not like writing for any other media. How we read on the web is very different from how we read a book or magazine or textbook or newspaper (remember those?).
When reading online, we tend to skip around
We use a different part of our brain (hint: it's a visual media!)
People have a short attention span
To best illustrate that last point, here is a scene from the movie 50 First Dates where Adam Sandler's character meets "10 Second" Tom, who has a brain injury that causes him to forget everything new he experiences after 10 seconds.
While readers may not forget everything in 10 seconds, that is about all the time they are going to put into reading your page unless you make the page more useful for them.
Some key points about writing for the web:
Get to the point!
Remove all unnecessary, extraneous information that isn't needed
Use easy-to-understand language
Avoid "marketese" or promo writing, jargon, and acronyms
Writing online is visual - use white space and keep paragraphs short!
Never use a metaphor, simile, or other figure of speech which you are used to seeing in print.
Never use a long word where a short one will do.
If it is possible to cut a word out, always cut it out.
Never use the passive where you can use the active.
Never use a foreign phrase, a scientific word, or a jargon word if you can think of an everyday English equivalent.
Break any of these rules sooner than say anything outright barbarous.
We could go on an on about how important it is to keep your writing simple and brief, but that would be oxymoronic, now wouldn't it?
"I have less than 30 seconds to capture your attention with this post, so ... if you read some, most or all of the next 750 words or so, you will know how to write Web copy that is more useful to readers of your blog or Web site."
Dave Copeland, journalist and college writing and journalism professor who writes about writing for the web
Write compelling but clear headlines: Don't get cute. Online and in print, the headline is almost always the first thing readers look at. Make sure it is clear and gives a good idea of what the post is about, while still leaving the reader wanting more.
Write in the active voice: Effective online writing is all about getting to the point, and on a line-by-line basis, the most effective way to do that is to use the active voice, which naturally lends a sense of urgency to your writing. The easiest way to do that is to start each sentence with the subject, immediately follow that with a strong, active verb, and then follow that with the direct object. Avoid adverbs: they're a telling sign that you chose the wrong verb.
Online writing is visual: Long, dense paragraphs turn off online readers. Create white space in your copy by keeping paragraphs short and using bulleted lists when appropriate. Use bold text to accent key information and use block or pull quotes to draw readers into the copy.
One main idea per sentence: Keep sentences on point. Avoid multiple clauses and phrases, and lots of information stops and commas. Make sure each sentence has one idea, and not much more than that.
No sentence without a fact: Every line you write needs to move the story forward. If a sentence doesn't have a fact, cut it.