Because the earth & moon are in motion, it's best to use relatively quick shutter speeds to capture detail on the surface. Try spot metering off the moon, then compensating the exposure a bit (+1 or so). Also, the best time to take the shot is early evening or morning when the moon is low in the horizon and the sky isn't dramatically darker than the moon.
This article talks about it and there are some good handheld samples in the 'comments' area.
The Online Photographer