So your boss just made 'copywriter' a de facto addition to your job description, and the only writing you've done since graduation is with To: fields or with two thumbs.

Take heart. With some basic guidelines (grouped by level of difficulty), you can make your writing easier to read and easier to engage than much of what's out there on the wild wild web.

Piece of Cake!
Avoid TL;DR.

TL;DR? It stands for "Too Long; Didn't Read." We read differently on digital devices: more haphazardly, less deeply, more selectively and less attentively. So the rule to rule all rules when writing for the web: keep it short, then shorten again, then shorten once more.

Organize your writing into digestible sections.

Reading large swaths of text is overwhelming. Writing them is tiring. As Karen McGrane says, create in chunks, not blobs.

Use your headers to label these sections.

Your H1-H4 headers aren't just important for search strategy. They also help your readers see how the pieces fit into the bigger picture. (This basic level of organization also helps you collect your thoughts and make better use of your archives.)

Write short, declarative sentences. 

There's no better way to build trust with your readers than to be clear and direct. And there's no better way to lose attention than to ramble on. This doesn't mean you need to skip steps — it just begs you to find the shortest path to each one.

Use bulleted or numbered lists.

In digital media where we scan rather than read, lists 

• are easier to parse
• provide a good natural constraint on wordiness
• segment text visually and conceptually
• encourage you to surface coherent patterns

Call a spade a spade.

Shakespeare said a rose by any other name would smell as sweet. Still, if you're a florist and someone orders a dozen sunflowers, you don't send a bunch of roses instead.

By that same token, be straightforward and clear when you name things on your website. Putting your press releases and media kit under "Paparazzi Fodder" might be cute or clever, but it's confusing for both users and employees. Putting them under "Communications" doesn't help either. When your users clicks, will she find news items? Blog posts? A profile of your communications team?

Titles as simple as "Press" or "Media Room" work without making people think. They also don't need to list every type of item therein: you just want a name to align your users' expectations with what they actually get.

Icing
Listen.

Having a hard time putting something into words? Listen to the way you explain it while talking to your spouse, your friends, your clients.

And listen to your support staff. They're some of the best people to chat with when it comes to explaining technical concepts: they can easily put themselves into your users' shoes, and they have thousands of calls and emails of practice honing the clearest, simplest explanations.

Keep it simple and friendly.

Think of a complex topic in your field. If you can communicate this to a gentleman across from you on a plane*, your explanation will (by virtue of being distilled and clear) appeal even to experts. 

Use this mental exercise to sharpen your writing — get rid of jargon, keep thinking of ways to simplify, search for illustrations that naturally resonate.

*Want to give this a try? Here's a neat widget, inspired by XKCD, to see whether you can explain something using only the 1000 most common English words.

Be confident and assertive.

If your goal is to solicit feedback and advice from your audience, do so.  Otherwise, you know your facts, your audience, your industry. So speak with that authority. (This'll help you with with those short, declarative sentences!)

Yes, write what you know.

So maybe you don't know your facts, your audience, or your industry. Do your research, and practice explaining it to others. Find the person in your company who's the expert on what you're trying to communicate. Ideally, she's the one who creates the foundation for this piece of content. But otherwise, interview her, and keep returning for feedback.