Don't insult your readers

I would wager that most of us do not sit up all night thinking of ways to treat our readers like they’re stupid. Yet, it is a common problem, especially with newer writers who are still learning the craft. All of us can slip into these nasty habits, if we aren’t mindful. (from here)

I love this article. It's written primarily from a serious, fiction-writing perspective, but it has some good points for all of us who write, and more of us are writing than ever before with social media. 

This is one to keep in mind:

Don't use punctuation and font as props. 

Especially be careful about exclamation points, ellipses, bold and italics fonts. Strengthen your writing before you use these as crutches to prop up your writing.