Having a rough interview? Even if you give stellar responses in an interview, an interviewer expects other things but never tells you.
Timing
Your answer should have ended five minutes ago.
It's natural to ramble when you're nervous, but know when to stop yourself before you begin to give TMI. Get to your point and stay on topic. If the original question was about your educational background and you're now talking about your freshman year roommate, it's time to shut up.
Know where the line between appropriate and inappropriate lies and do not cross it. This doesn't just mean being polite, but also professional. If your last boss was terrible and you're asked about him, focus on flaws with his managerial style, not his personality or character. This is an opportunity to tell the interviewer what type of relationship you prefer to have with a superior, not bash an old boss.