Watch What You Write or Say. Assume that anything you write or say will be read or heard by everyone in the company. E-mail makes it easy to respond emotionally. Before you respond to an irritating e-mail, take a minute to calm down, then, write the e-mail. If you have a tendency to send harsh messages, save a draft and review it sometime later to ensure the tone is business appropriate.
A corollary to this principle is Happy Hour - don't go! There is a huge risk of saying something you shouldn't say, getting out of control, or just being in the wrong place at the wrong time. You should stay out of office politics. Don't say anything bad about anyone, ever.
Arrive Early and Leave Late, but Not Too Late. You want the reputation of a hard worker, but not one that can't get their work done. This principle also applies to taking work home. Over the long-term, you want to have a life outside of work. Maintaining a work/life balance will keep you engaged in your job; therefore, more productive.