Yawning is canine for "peace." I use calming signals with Ava. When she is hyped up, I look away and give a few big yawns. When I get her attention, I will yawn, then blink very slowly at her. Sometimes, it takes a minute if she is in overdrive, but she will usually slow down and watch me. Eventually, she yawns back. Then I can pick her up and give her calming strokes. As agilebasenji mentioned, the Turid Rugaas book/DVD is very helpful.
I have learned to recognize Ava's main stress signals– opening and closing her mouth, licking her lips, rigidly turning her back on me. When I notice these, I can use calming signals to reassure her. Sometimes, after we go through our spiel, she'll put her paw on my hand and look at me as if to say, "I'm cool now, mom." Of course, sometimes, nothing works.