High school composition classes tend to lump a lot of rules into writing—many of them telling writers what not to do. But you're not writing to please your teachers anymore. Many of those prohibitions refer to the so-called mistakes that occur naturally in speech. I encourage you to safely and fearlessly break those rules and to make those mistakes in writing—but only when doing so lends greater clarity and readability.
- Never start a sentence with and, but, or because. And why not put and, but, or because at the beginning of a sentence? Because Ms. Dolan didn't like it? That's the way I heard it, anyway. But now that I'm a grown-up I realize that she was wrong. Why? Because all three can add energy and momentum to a piece. They can keep the action moving from sentence to sentence.
- Avoid sentence fragments. It's perfectly fine to sparingly add sentence fragments for emphasis. At least, sometimes. (Like that.) (And that too.) (And this.)
- Never split infinitives. There's supposedly a rule that says you can't let anything come between to and its verb. Mignon Fogarty (who runs GrammarGirl.com) says this is an imaginary rule. She writes, “Instead of ‘to boldly go where no one has gone before,’ the Star Trek writers could just [as] easily have written, ‘to go boldly where no one has gone before.’” But they didn't. You, too, can split if you wish. But be careful not to change the meaning or create too much ambiguity, as Grammar Girl ...