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I've tried the ones about tensing muscles for willpower, crossing arms for persistence, smiling to make myself happy, and taking up more space to seem dominant and they seem to work. I find a hearty laugh is also good at inducing happiness.

I used to have a habit of trying to preempt people in saying what they were trying to say. It helped me understand math, but a few of my friends and family members found it irritating. So now I do more mirroring.