Last winter I got five colds, each lasting two to three weeks. The winter before that, I got four, and every winter I can remember before that I got three colds. Two winters ago I tried an experiment. I washed my hands religiously and didn't touch my face at all. I had hand sanitizer with me at all times. It didn't help at all. I asked my doctor what to do and he said wash your hands.
Last fall when the cold season started I got a cold. Around the time it went away I started taking 200mg vitamin C every night before bed. I have not had a cold since. This might be anecdotal but I am now a big believer in vitamin C.