Don’t say or write anything you wouldn’t want made public. You have zero expectation of privacy at work & should therefore assume that anything & everything is being recorded & will come back to haunt you at the worst possible time. That includes emails, phone calls, even hallway or parking lot conversations.
Don’t over-apologize. We all make mistakes and it’s always good to fess up, but in business, you can go too far and actually make matters worse. If it’s a minor issue, just a quick “sorry about that” is fine. If it’s a big screw-up, apologize in private, face-to-face. Look the guy in the eye, say your piece, and be done with it. Don’t grovel, make promises you can’t keep, or anything else. Just man-up and leave it alone.
Don’t make commitments you can’t keep or exaggerate your ability or influence. And don’t lie, either. The more straightforward and genuine you are, the smoother your career — and your life, for that matter — will go. Do what you say you’re going to do and leave the BS for the other guy. Your credibility will grow, people will count on you for more and more, and off you go.
Don’t whine and complain incessantly. If you’re a big crybaby, nobody will want to have anything to do with you. It’s ironic, but those who do all the complaining are the ones who make the workplace a living hell, not the people or stuff they’re always whining about.