The reason to use a lens hood

Hoods that come with good quality lenses are designed to reduce glare on the lens when shooting outdoors in daylight. But many photographers, including pro, keep using it in indoor, with reason, to protect the lens.

The glass lens, almost parallel to the end of the barrel. When the lens is in contact with something, and this object was not soft, your lens will be scratched, in worst case it could be broken, addition lens hood can also prevent stains fingers, because we accidentally touch the tip of the lens.

Tips Camera Maintenance

1. Avoid dirt and sand. Use care when cleaning dirt particles and sand from your digital camera. Do not use canned or pressurized air to clean the sand, as you might just drive the particles into the camera case. Budget priced camera cases might not be sealed perfectly, making it easier for grit and sand to penetrate the case and cause damage. Gently blow out the grit and sand to avoid this problem. Use care when shooting photos on a windy day at the beach, too, where sand can blow with excessive force. Avoid opening the battery compartment on such days.
2. Avoid liquids. Try to keep all liquids away from the camera, unless you have a model with a waterproof case. Cameras are like any piece of electronics, and they can be damaged by excessive water.
3. Avoid touching the lens and LCD. Oils from your skin can smudge the lens and LCD, eventually causing permanent damage. Clean the lens and LCD with a microfiber cloth as soon as possible anytime you see a smudge from your fingertips.
4. The lens and sun don't mix. Do not point your camera's lens directly at the sun for any length of time, especially with a DSLR camera. Sunlight focused through the lens of the camera could damage the image sensor or even start a fire inside the camera.
5. Use cleaning liquids with care. Avoid using an excessive amount of cleaning liquid with your camera. In fact, other than stubborn smudges, you should be able to clean the camera with a dry microfiber cloth. If a liquid is needed, place a few drops of the liquid on the cloth, rather than directly on the camera. Water can be used in place of cleaning liquid as well.
6. Vacuum the bag. Dirt and sand inside your camera bag could damage your camera, so be sure to vacuum the bag regularly to keep it clean and protect your camera.
7. Watch the temperature. Although some cameras are designed to survive harsh temperatures, most cameras are not. Do not leave your camera in a sunny vehicle, where temperatures quickly can exceed 100 degrees Fahrenheit. Avoid leaving the camera in direct sunlight, which can damage the plastic. Finally, avoid extreme cold, too, which could damage the LCD.
8. Use neck straps and wrist loops. Admittedly, this is more of a "preventative" maintenance tip, but be sure to use neck straps and wrist loops with your camera whenever possible as you're shooting photos outside. If you slip while hiking, or if you lose the grip on your camera near the pool, the straps can save your camera from a potentially disastrous fall. Better safe than sorry.

Digital camera maintenance doesn't have to be difficult. These simple tips show that keeping your digital camera clean can be fairly easy and can help you keep the camera in working condition as long as possible.

source  http://cameras.about.com/od/troubleshooting/a/maintaining_cameras_tips.htm