When should i keep the lens hood on my camera?

So basically i have a lens hood for my kit lens 18-55 on my nikon d3100.

In which cases should i keep it on the lens?
Always when i'm shooting?
When there's too much light or the sun is fasing the camera?

Depends what your shooting, the good will block out any sunlight that you don't want and when your shooting in the middle of the day or in bright day light you should have it on so you don't get Nasty glare on your photos.

I keep the lens hood on my lenses all the time, indoors or out. Of course there's no reason to expect harsh side light indoors like outdoors but it is just a good practice as is always using a Uv filter as a protection filter, plus I only have to clean the lens once or not at all if it came to me new or clean in the first place. Another thought is that heaven forbid you drop the camera (hopefully from a short height) you will probably bend the lens shade making it unusable. But bend the lens mount and you are looking at an expensive repair plus doing without your lens for 6 to 8 weeks.

The only time I take off the lens hood is when I'm going to stick the lens to the glass walls in aquariums and glass windows of snake pits at the zoo.