Maybe ask others for your signals.

For me, I tend to talk faster, raise my voice a bit, frown more, and generally behave more combatively.

So basic things like slowing down, relaxing my expressions and smiling more (even and especially when you're on the phone!!!) go a long way to not only changing how I present myself, but also changing how I feel.

Meditation. It is the practice of being present in the moment and being aware of your actions. That directly translates into "catching yourself" by requiring you think about everything you do before you do it and be aware of what you're doing in the moment.