Hey Doc

Even in digital age, the Sunny16 rule for proper exposure is still apply.
The shutter speed is the reciprocal of the ISO setting on your digital camera. If you are shooting at ISO 200, the shutter speed should adjusted to 1/200. This rule applies to daylight only, can't used with flash or studio lighting. Apply minor tweak if your camera does not have the exact setting according to the formula.

Snow or sand - F22
Sunny - F16
Slight overcast - F11
Overcast - F8
Heavy overcast - F5.6
Sunset or open shade - F4

Another tip on the shutter speed, this has to do with handhelding the camera. The minimum shutter speed without causing blury image is the reciprocal of the focal length of the lens. Say, if you are using a 200mm lens, the minimum shutter speed is 1/200.