Share the emotional burden of others
For the most part, we can keep control of our emotions. Sometimes emotions get stronger though, not only for ourselves but for others too.
There is a simple method to improve the experience of someone feeling strong emotions, and it's merely to use empathy.
Share in their emotions. Listen to what they have to say and be supportive.
This works with both positive and negative emotions. Think of something bad happening and it's just like the quote - 'a problem shared is a problem halved'. By bearing some of the negative emotional burden of another, you can lighten their emotional load. You're someone they can confide in, share themselves with and generally lean on for support because they feel understood.
On the other end of the spectrum, this works when someone's celebrating success. If you're sincerely proud, it magnifies positive emotion because you're giving the approval everyone craves.
To build this empathy, practice removing yourself from your mind and thinking about others more often. Think about how you can best understand how they're feeling. This makes it easier to divide (in the case of negative) or multiply (in the case of positive) emotions between you.
I suggest you only attempt to share in the emotional burdens of people close to you.
Emotions are potent.
When you share a negative emotional burden you'll feel more negative because you're bearing some emotional weight. When you share in a positive emotional burden you want to make sure that it's on behalf of someone you have a vested interest in seeing succeed. It would disrupt your calibration of success if you were overly invested in the success of people who aren't close to you.
Increase empathy with others to improve their experience by bearing their emotional burdens.