The beauty of newer digital cameras is that you can change your ISO rating "on the fly" when your lighting situation changes.
For example: You're out in the yard photographing the kids in bright sunlight or snow (yikes) with your camera set to ISO 100.
Next, you decide to go into the house to take pictures around the dinner table or next to the fireplace; this would be a great opportunity to change the ISO setting on your camera to 1000 to allow more light to be recorded by the sensor.
- ISO 100 For bright outdoor scenes
- ISO 200 For activity in the sun and shade
- ISO 400 For fast action scenes under mixed light situations
- ISO 1000 and higher For fast action in very low or mixed light situations.
This list represents a general starting point. I always recommend trying different settings on your camera until you get the results you desire.