As the manager, you are the representative for your business and your staff. That means you need to maintain your dignity even when you're not on the clock. Whether it's a business trip or the office holiday party, keep your behavior professional. Speaking of holiday parties, don't get crazy even if alcohol's involved. In fact, don't get crazy especially if alcohol's involved.
When travelling for business, remind yourself you're not on vacation. Bump your attire up a notch and dress formally. It's not the time to break out the sweatpants or speedos. Don't drink too much on business trips either, particularly if junior staff is present. You want to set an example. When you're on international business trips, check up on etiquette for the region and brief your staff. They need their manners intact, too.
Social media is another after-hours activity where you need to maintain control. Make it a practice not to friend your employees and keep your accounts set to private. Even if you're not on social media, what you do outside of the office can often end up there. You may never live it down and might even lose your job.