1. Don't do it anywhere noisy, like at Starbucks, or with your kids in the room. Background noise can hurt your chances of getting hired, because it's distracting. And make sure you're somewhere with good reception too.
2. Don't be late. You should never be late for ANY type of interview. But there's no excuse when it's over the phone. So make sure you pick up when they call. Or if you're calling them, do it exactly when they asked you to. Not five minutes early, or late.
3. Don't try to multitask during the interview. You'll sound distracted. And it's more obvious than you think. So focus on the interview, and nothing else.
4. Never put them on hold. They should be your top priority. So let all other calls go to voicemail. And you shouldn't even have to ask them to hang on while you go grab a pen or something. You should be prepared going in.
5. Don't talk over them when they're finishing a thought. It's more obvious over the phone than it is in person. So let them finish what they're saying before you respond. And try to be clear and concise without rambling too much.