While we can all agree that's not a good thing to do, the idea of parking your emotions at the door when you show up for work is entirely unrealistic. After all, compartmentalizing your emotional state is more or less psychopathic, as any good shrink could tell you.
Step 1: Awareness. Before you walk into work or a meeting, try to discern what you're feeling. It's not as obvious or simple as it sounds. The human mind is very good at burying in the subconscious what the conscious mind may not want to deal with. What you want to determine is if your mood is either significantly better or worse than usual.
Step 2: Understanding. Once you determine that you're feeling something unusual, whatever you do, don't try to ignore it or think it away. Emotions are critical signs of what's going on inside you. Instead, try to find some alone time and get to the bottom of what's really going on.
Step 3: Motivation. As we discussed in the first story above, sometimes emotions can be powerful motivators. They can drive you to do great things, perhaps to prove to yourself what you're capable of doing in spite of the obstacles. On the other hand, if you're not as self-aware, that's when you become your own worst enemy.
Step 4: Behavior. If you know you're dealing with some unusual emotions, try to be aware of your behavior. You might be more grandiose or short-tempered than usual, and that's important to know so you can give others a heads up and pay attention to feedback. If they see what you're not aware of, that's not a good sign. Don't just brush it off.
Whatever you do, don't use employees, coworkers or customers as either emotional punching bags or as personal confidants. Not only is that crossing a line, it's self-destructive behavior because, on some level, you know it's wrong and you're doing it anyway. And that means you're not as self-aware as you might think you are.