One strategy particularly struck me: if you’re feeling a negative emotion, you can work to reduce it by labeling it in one or two words. Note, however, that thinking or talking at length about the emotional state tends to intensify it — while simply observing and labeling it helps to quell it.
I do this myself, instinctively. I find myself thinking, “I’m overwhelmed” or “I’m frazzled” or “I’m feeling defensive” — and it’s odd how calming it is. Just putting a label on a feeling helps me to master it.