Some simple rules that I have found:
Write well, write little. Brevity is the soul of wit and genius is the foundation. If you can write a long piece that explores a concept, write something short. Don't run out of good prose before you run out of material. If you read the piece and it's weak: condense. The difference between gravy and broth is condensation. People like short punchy online pieces. We're used to changing channels when we stare at screen. People get fidgety when looking at the computer. Also, books don't glow. Unlike a book, you have to put yourself where the computer is. All this equates to an uncomfortable experience. Their tolerance for online reading is less than the paper world. If you could slog through a 20,000 word (40 page) treatise on paper before petering out, the same subject matter may only hold you on screen for 6,000 words (40 screens) or less.
Timely, colorful and buzzworderiffic. When you write speak to your audience but don't forget that they are tied to pop culture is some small way. Leverage that tie. Throw in references to timely issues and pop culture where such would fit. In other words, don't liken the oil prices to Jessica Simpson's ample qualities and housing starts to Peter Jackson's shrinking waistline. But you can get away with some of the longer lasting cultural touchstones to keep your material from being dated. Why? Why mention the Rolling Stones in your piece on perscription medication for seniors? Google. There are about 20 words and phrases from this article that will make it into the search engines (well: it all goes in and gets ignored) and few of them are about "content." When you visit Google, type in a keyword and find hits, you are not taken to the site you seek: you are taken to Google to see what you selected and then taken to the resource. A popular site becomes more popular. Throw in buzzwords and you can benefit from accidental traffic. Keep this concept low key however: if non-sequitor hits form the bulk of your traffic, your traffic rank will fall.
Unseen qualities. If there are any important points in your article, emphasis them with the "title" attribute. The title attribute can be slapped into almost anything: images, hrefs, spans, etc.. When you users mouse over a section, they can get additional information. I like the < span > tag. It can be innocously added.
This is an example
< span title="This is how to code it with a title tag" >This is an example< /span >
I like titles but search engines LOVE titles. It's good form, it helps users and it will raise your profile.
Metered novelty. People like new content. They like it so much that they will return if stuff is new every time. I'm a geek. I visit three sites regularly: TrekToday, Force.net and Cruel.com. They all have two things in common: new content daily and they probably get more pieces than they publish in a day. Newspapers have editions. When the paper is full, stuff gets bumped to the next day. Do the same. Of course, you might not have time to do a daily edition. You might only have a few hours on the weekend and a couple of hours through the week. This is where a content management system really earns its keep. Some products can time content release. You can set up a number of pieces, time the release date and let it go. Monday and Tuesday roll by and your items pop onto the screen like magic. Whenever I've built a tool for content delivery, I usually push really hard to have this feature.