What a great topic. I use imagery and mental training in my spin classes all the time. The group i train on a regular basis have told me they really like it.

A couple of things i do: finish the following sentence:
"I am..." as in I AM strong, I AM powerful, I am as fast as a...they have fun with that one.

the other thing i tell them, don't just think you can, KNOW you can.

MAKE it a good day. don't just have one.

My favorite quote out of Women who run with wolves: It is not the failure that holds us back but the reluctance to begin over again that causes us to stagnate. if you’re scared, so what?

and one to make you giggle:
You know that old proverb about how it takes more muscles to frown than to smile? Ride angry: it's a better workout.