When writing for the web, focus on the things that the web does better than print.
Use links to direct readers to related articles, background information, and the source of your information. Why settle for including only a small quotation when you can send your readers to the entire article? Clicking a link is a lot easier than driving down to the library to find the book or article in question. You can also use internal links, which make it easier to move through a single document or connect to other pages within your website. Google Docs, for instance, has a table of contents feature that will link together all the parts of your doc. If you have a blog, you can link to earlier posts that are relevant to what you’re talking about.
Writing for the web means thinking about all of the different contexts in which your stuff can be found. That’s why it’s important to always title your work. In addition, once people arrive at your pages, you have broken big chunks of text into smaller sections, with section headings, so they can find what they want quickly. Anything that takes longer than 10 minutes for the average person to read should be broken up into multiple posts or sections. Instead of thinking in terms of articles or essays, try to think more about paragraphs (blogs) and sentences (tweets).
Writing for the web also means that you are part of an information ecology. Other people may find your writing through a search engine or an RSS feed. They can easily search your text for keywords or zip instantly to a chapter or section.
Writing for the web also has built-in community features—it’s a lot faster and easier to get feedback from your readers and have discussions about your texts when you put them online. Communities are what make writing for the web so much fun! Before, authors had to wait weeks, if not months (or even years!), to get feedback on their work. By that time it was old news. Now writers can post a blog and get comments in only a few hours or less. Interacting with your audience will help you tailor your writing style and topics to better suit them, so pay attention to what they say.
Writing for the web also means writing with media. You can include color, images, and videos with your texts. You can include animation and sound. You can write with the white space around words and play with designs to better show off your stuff. You are no longer turning in grey pages of text to a professor; you are writing to a real audience, and you need to use all the tools available to connect with that audience and show them that you share their values.
In addition, the web is no longer accessed only on desktop computers and laptops. Visitors to your site may be using a mobile phone’s smaller screen, which means they will have different needs than readers using a full-size monitor. Conversely, Internet TVs are becoming more common, and before long, many people will use iPads or Android tablets as their primary device for reading the web. With such variety in screen sizes and resolution, the challenge becomes making sure your content looks good across multiple web browsers, platforms, and devices. Since you can’t be sure how people will access your stuff, keep the design elements simple so that browsers can accommodate it.