Wash your hands. With soap and water (or alcohol-based sanitizer if not available), in between your fingers, paying close attention to the tips, for at least 20 seconds. Channel the god Judi Dench as Lady Macbeth if you have to.
Refrain from touching yourself. You should avoid touching your eyes, nose, and mouth if your hands aren't washed. (If they are, wash them again.)
Avoid people. Colds may strike in the winter, but there's little evidence that cold weather itself contributes to their spread. What's more likely is that people huddle up in large indoor groups in the winter and all our collective flesh piles trade the viruses like Pokemon cards. Don't hang out with folks who have colds.
Whatever, people suck anyway. Pour your sickly self a hot toddy and enjoy the night in.