Keep doors shut. Wear a few thin layers of clothing rather than a couple of thick jumpers. Put a scarf on (even indoors, this can make a big difference). Have plenty of fluids. You will be suprised how warm you can get from doing household chores. Now is the time to do all those jobs you have put off. If going out. Hat, gloves and the all important scarf.
sathy, indoors or outdoors ? Or do you mean how to avoid GETTING a cold? If it is the latter, when you are near someone who is sneezing (I would suggest all the time) take a couple of Echinacea from Holland & Barrett, then each day for a week take another one. This helps build your immune system up (it works with me anyway) but don't take them for more than a week. Only when someone near you is ill or you feel like you are getting 'something' e.g. a sore throat.