Drinking plenty of water and taking vitamin "C". I never have colds because if I feel the slightest evidence of a cold starting to come, like a sore throat or runny nose, I squeeze organic lemons in my water and eat the pulp. And just like that there are no more symptoms.
For those who waited until they have a full blown cold. Eating lemons all day and drinking plenty of purified water will take your cold away. I've done and people I recommend this to tell me they can't believe how much they feel better the same or next day.
Try it - you'll feel better, I know!