The most important thing you can do is keep your hands clean and try to avoid touching your face, especially your eyes and nose, because that's how people give themselves
There are hundreds of viruses that cause the common cold, but they almost all need to get into the mucous membranes lining the nose in order to cause infection. The nasopharynx -- where the nose meets the mouth -- is the "sweet spot" for cold viruses. A virus deposited at the base of the nose or in the eye can easily be inhaled higher up into the nose, or drain from the eye into the nasopharynx through the tear ducts. So keep your hands away from your nose and eyes; if you don't deposit a cold germ there, you'll have fewer colds.
Unlike influenza viruses, most cold viruses are hard to transmit through the air only. If the first exposure is to the mouth or lungs (for instance, if you kiss someone with a cold or a sick person coughs on you), it's much harder for the cold virus to get to the nose.
Studies have shown that most cold viruses can survive for up to three hours on nonporous surfaces such as doorknobs, countertops, and coffee cups. They can also survive for several hours on people's hands if they aren't washed off.
This means that you're far more likely to catch a cold from putting an infected person's water glass in the sink, and then wiping your eye, than you are from not touching the glass but being given a sip of the sick person's water.
Another odd fact: Cold viruses don't survive well on facial tissues and cloth handkerchiefs unless the mucus is still wet. Still, if someone in the household is sick, it's a good idea to dispose of their dirty tissues promptly. A recent study also found that there was less spread of colds in families that frequently used alcohol-based hand gels .
Many people also turn to supplements to try to prevent and treat colds, but it's not clear that these really work. The best studied are vitamin C, vitamin D, vitamin E, zinc, echinacea, and garlic. Although many people swear by the effectiveness of some supplements, and some studies have been promising, to date no supplement has been definitively proven to help prevent colds.
What does help? Sleep. A recent study found that people who sleep more had better resistance to infection from cold viruses.