When to Use Higher ISOs

Here are some examples of when you might want to set a higher ISO sensitivity. in every case, set the lowest ISO that will enable you to use the settings that you need

Shooting handheld at dusk or on overcast days when it isn't bright enough to use a shutter speed higher than 1/60 sec with your standard lens. (At speeds slower than this the risk of camera shake becomes greater.)
When you are using telephoto lens and there is not enough light to use a shutter speed that us at least as high as the focal length your lens is set to. (For example, if using a lens set to 200mm, the shutter speed should be at least 1/200 sec to reduce the risk of camera shake)
When photographing fast-moving subject and the light isn't bright enough to use a shutter speed quick engough to freeze the motion.
When using flash and the flashgun isn't powerful enogh to correctly expose your subject - either becaouse it's so dark or your subject is too far away.
When you're shooting indoor, and flash is either prohibited, or would be obtrusive (such as at a live performance) or would destroy the atmosphere created by the ambient lighting.
When you need to use a small aperture to create a wide a depth of field, but doing so gives a shutter speed that;s too slow to handhold.