There are a few generally understood guidelines when writing for the web. These guidelines include short, scannable pieces that are search engine optimized.
Keep it Short
The principle for short writing is to write 50% less text than you would on a hardcopy. Readers also don’t like to scroll or navigate to further pages and don’t have time to sit down and dedicate time they don’t have to long content. You do not want to bore readers.
Make it Scannable
The fact that people’s attention spans have gotten shorter and shorter with web browsing, the reader wants to be able to scan documents. Writing for the web can be made scannable through structured headlines, the use of italics, bolding, & underlining to emphasis important words, and using hypertext. Hypertexts help keep the writing short and interactive for the reader.
Search engine optimization is important for getting readers to the content. Most people find articles by Googling topics and keywords. The fundamental elements of SEO writing is keywords and phrases. Keyword density should be kept around 4%. Web writing should also be organized and simple being kept around 300-600 words.
For Longer Content
On the other hand, the shorter the article, the more risk of not getting the point effectively conveyed. Sometimes content needs to be longer to get the point across, and other times readers want more because of the quality of the content. Good content is going to make readers want to keep reading, even if it is online. Longer content answers more questions and goes into more depth. People who are truly interested will keep reading. Here is an example of an interesting, compelling article about conjoined twins that kept me interested even with the lack of traditional web writing elements.