Here are five mistakes to avoid when blogging and writing web copy:

1. Your vs. You’re – This one drives a lot of people insane, and it’s become extremely common among bloggers. All it takes to avoid this error is to take a second and think about what you’re trying to say.

“Your” is a possessive pronoun, as in “your car” or “your blog.” “You’re” is a contraction for “you are,” as in “you’re screwing up your writing by using your when you really mean you are.”

2. It’s vs. Its – This is another common mistake. It’s also easily avoided by thinking through what you’re trying to say. “It’s” is a contraction of “it is” or “it has.” “Its” is a possessive pronoun, as in “this blog has lost its mojo.” Here’s an easy rule of thumb—repeat your sentence out loud using “it is” instead. If that sounds goofy, “its” is likely the correct choice.

3. There vs. Their – This one seems to trip up everyone occasionally, often as a pure typo. Make sure to watch for it when you proofread. “There” is used many ways, including as a reference to a place (“let’s go there”) or as a pronoun (“there is no hope”). “Their” is a plural possessive pronoun, as in “their bags” or “their opinions.” Always do the “that’s ours!” test—are you talking about more than one person and something that they possess? If so, “their” will get you there.

4. Affect vs. Effect – As with any of the other common mistakes people make when writing, it’s taking that moment to get it right that makes the difference. “Affect” is a verb, as in “Your ability to communicate clearly will affect your income immensely.” “Effect” is a noun, as in “The effect of a parent’s low income on a child’s future is well documented.” By thinking in terms of “the effect,” you can usually sort out which is which, because you can’t stick a “the” in front of a verb. While some people do use “effect” as a verb (“a strategy to effect a settlement”), they are usually lawyers, and you should therefore ignore them if you want to write like a human.

5. The Dangling Participle – The dangling participle may be the most egregious of the most common writing mistakes. Not only will this error damage the flow of your writing, it can also make it impossible for someone to understand what you’re trying to say.
Check out these two examples from Tom Sant’s book Persuasive Business Proposals:
After rotting in the cellar for weeks, my brother brought up some oranges.
Uhh… keep your decomposing brother away from me!

Featuring plug-in circuit boards, we can strongly endorse this server’s flexibility and growth potential.
Hmmm … robotic copy written by people embedded with circuit boards. Makes sense.

The problem with both of the above is that the participial phrase that begins the sentence is not intended to modify what follows next in the sentence. However, readers mentally expect it to work that way, so your opening phrase should always modify what immediately follows. If it doesn’t, you’ve left the participle dangling, as well as your readers.