I've just done a brief scan of the Web looking for sites about writing. I was actually looking for blogs on writing - I'm sure they must exist - but didn't have great deal of success. When it comes to Web searches, I'm something of a bonehead.
The sites I found, most of which were not blogs, shared a few things in common. Despite using some terms and phrases about "online writing" and "Writing for the Web," most seemed to be by clods who have just discovered 1) the Web, 2) writing or 3) both.
There also seems to be some confusion. For those who haven't noticed, there is more than one kind of site on the Internet. In fact, there is a great deal of variety out there. The way you write is not conditioned by the Web, or at least not entirely. While it's crucial to be aware of the way people read online - scanning, rushed and with lowered comprehension levels - it is just as crucial to understand why they are reading.
In other words, people online are task oriented. So it's important to know what that task is. In some cases, the task is to read. (I'm not, however, arguing for loads of text. You seldom go wrong being brief and concise.)
So ... On some sites, such as business sites (product information, e-comm tools etc.), they are looking for information or looking to buy. On other sites, however, they are looking for news, sports stories, etc. Sometimes, such as in blogs, they are looking for people and ideas. And on some sites, such as galleries and so on, they are looking for images.
Some of these sites will have quite a bit of text; some will have very little. Some will be dry and direct; some will have personality and humour (or even crankiness).
In all cases, most general writing rules apply - just as they do anywhere else. But they are informed by the fact the text is a vital part of the layout. The visual impact of a page, more so than in other media, helps or hinders a person's desire and ability to read. As mentioned above, writing rules are also conditioned by the way people behave online - impatient, lower comprehension levels etc.
(By the way, have you noticed how the first two paragraphs of this bit are completely unnecessary? Or how I could have trimmed this thing down to half the length it is?)
I hate the word rules, especially when related to writing. In many ways, I don't believe in them. As soon as someone says, "The rule is ..." I want to break it. But ...
The good thing about developing and learning rules is this: they can be broken. However, it's only in understanding why the rules exist that you can break them without looking like an ass. This is because, if you're smart, the way you break a rule takes into account the broken rule's "why." You may also find, in the situation where you are trying to break the rule, that it cannot be done.
And that's my off the cuff musing about writing, the Web and rules. (And whatever else I may have thrown in here.)