Master your mind to control your emotions.
Emotions fuel thoughts.
Thoughts fuel emotions.
A cycle that quickly spins out of control if you let it.
If you're someone that struggles to focus when external events and the resulting emotions creep in, you must learn to master your mind.
This starts with creating space to do so; you cannot master your mind when it's been spinning for the last 8 hours.
So before all else, take a moment to bring yourself to the present moment.
Then remind yourself that you are in the driving seat, not your mind.
Leading happiness expert, Mo Gawdat, calls his mind Becky. Almost to say "I am not what goes on in my mind" which allows him to disassociate from it.
One of the most life changing book's I've encountered, The Power Of Now, describes this as "watching the thinker" - catching your thoughts like you would a child being mischievous.
This requires practice, but in time shining a light on Becky means that she loses her power.
This will of course be an ongoing battle, especially if you are an emotional individual or a certain event triggers a lot of emotion.
Stick at it, stop the cycle before it spins out of control, stay focused.
Oh, and read The Power Of Now.