Why is there a specific article on how to write for an online audience? Can't you just write like you'd normally write? Well, no, and here's why.
People read differently online than they read paper.
People read things on their computer screen differently than they do when they have a piece of written paper in front of them. Instead of cozying up on the couch with fuzzy slippers, a warm blanket, and a good book, people read web pages rapidly. They read to find a piece of information. So, they scan instead of read. They get distracted by instant messages and email. And they don't read in an orderly manner.
Firstly, people searching on the web are looking for information about something that interests them. Most of these searches are for casual information. Imagine you're sitting at the dinner table with your spouse and someone says "bla bla bla pumpkins." The other person says, "I wonder how long it takes pumpkins to germinate and then fully mature?" So, one of them goes over the computer and types in "pumpkins germinate full-grown fruit." That person wants two specific pieces of information and isn't going to read a dissertation on the growth of pumpkins. People like short articles. They will scan your article, not read it.
Write like a newspaperman.
Because people scan for information, put the important stuff at the top of your article. Write like a newspaper reporter and don't "bury the lead." Write each sentence as if that is where the reader will stop, putting the important stuff on top and less important stuff on the bottom.
Make it easy for your readers to find what they want.
Help people scan (and therefore make them like your site better) by using information-filled headers. Readers tend to be drawn toward the headings, so make it easy on them. Also, readers don't like big, long paragraphs. Make your paragraphs short. Make your sentences short. Make it easy for that guy to find out how long until pumpkins germinate.
If something is really important, put it in a short paragraph and surround it by a lot of white space. The white space draws attention to it. Don't make it in a large, bright red font with a lot of exclamation points. That just makes it look like an ad, and people are experts at avoiding ads.
In summary, here are some good rules of thumb for online writing.
1. Use lists.
2. Use plain text, but it's okay to bold once in a while.
3. Don't write copy that looks like an advertisement.
4. Get rid of unnecessary words and cut your article to half the size it normally would be.
5. Keep to one idea per paragraph.
6. Keep blocks of text (like paragraphs) small. Keep sentences short too.
7. Use a font designed for onscreen reading, like Verdana.
8. If something is important, surround it with white space.
9. Use subheadings with meaningful, information packed words.
10. Get the most important information in the first paragraph.