Colds are usually caused by getting a chill or getting infected by someone else.
Everyone has given you good advice so far, but nobody mentioned LEMON.
I have found a hot lemon drink like Beachams plus fresh Garlic (not capsules) very effective.
I used to suffer from many colds over winter so I tried an experiment and took a hot lemon drink
with fresh Garlic and honey every day and didn't have a cold for 3 years. I only stopped it because my wife
couldn't stand the smell of Garlic any more.