How do you calm down a high spirited mare?

Lunge, lunge and lunge some more! Also, talk to the horse lots, and if you're riding a frisky horse out I would suggest some light schooling (or lunging!) beforehand, just to take the edge off. And try doing some 20 metre circles, they're always useful.

I agree with above. Frisky horses are those that often have not had enough exercise, or have a high-energy demeanor. Putting it on a lunge line and giving it a good run in the round-pen is the best way to drain a bit of that pent-up energy, if you can't saddle it up and take it for a good run or a long walk.