When you screw up something, call someone, say “I screwed up something, can you help please?”
If someone else screws up something and it’s possible for them to fix it, give them a chance to fix it and don’t act like you’re above making mistakes. Thank them for their work in fixing it even when it’s their mistake. Heck, ESPECIALLY when it’s their mistake. You want employees, customers, and vendors to think that they can admit fault and work with you for a solution rather than feeling like they have to hide it.
Compliment people for their work when you can, for their demeanor when you can, and for their anything else you can reasonably compliment them for. “You do good work,” “I don’t think you get enough credit for your collating skills,” “You make this workplace less of a hellhole.” Don’t go overboard, but find positive things to say to people about what they bring to the workplace or the world. “You’re always so helpful, you make it easy to order string!”
If you’re ever considering doing something to teach someone a lesson, don’t.
If you have an assistant, treat him or her like something precious and valuable. THEY ARE.
If you say you’re going to call someone back, call them back. I had a boss who would tell me to tell people he would call them back, then find an excuse not to call them and have me call them with that excuse. I hated that, and the people we were dealing with hated it.
Take notes.
Keep gossip to a minimum and don’t badmouth bosses, underlings, other employees, customers, or anyone you regularly do business with in the workplace. If the office develops an attitude toward a customer or a vendor or a government agency, that attitude WILL come out in future dealings. Don’t get into the habit of holding anyone in contempt.
Show up on time. Always.
Even in a business deal where one side says “All sales are final” or something equally daunting, if something goes wrong, try to negotiate. Don’t be a dick about it just because you can or just because you’re desperate.