At the risk of sounding really trite on an Oprah level, I'm going to suggest smiling more. I was in a tough meeting earlier this week, and there were a few times where I had to invoke my miracle of mindfulness "half-smile superpower". There were a few times where I should have invoked it and I forgot!
This is something I read about in Thich Nhat Hanh's The Miracle of Mindfulness. Picture the Mona Lisa's half-smile. It's a smile that evokes "humor, serious but not too serious, non-commitment to a response, open, opening to others to share in the smile... an attitude of humor and openness to others and the universe".
It's not a pinched sarcastic smile, it's not a "flip" smile, or a coy smile, or a smug smile, or a fake smile, or a grimace. Nor is it the kind of smile you'd make after hearing a joke. It's not much of a smile at all if you see it in the mirror. Actually nailing the half-smile is part of the challenge. Because if you're feeling pinched or sarcastic or fake or smug, it won't work. So you kind of have to modify both your face (your outlook) and your attitude (your inlook?) at the same time in order for this to work. But that's sort of the point.
What I like about this technique for dealing with stress is that you can remain engaged. I saw another person in the meeting deal with stress by becoming argumentative. (They are perhaps still engaged, but at what cost? I did this once myself but managed to squelch the tendency the other five times I wanted to do it...) Another person left the room several times. A third person withdrew and looked at the floor or doodled. The cool thing about the half-smile is that it not only sends the right message outward but seems to actually cool the mind inwardly as well. You can't maintain a proper half-smile in anger.