At early signs of cold:
I don't take a medicine immediately, besides that I want to protect my body from being too dependent to medicines, they're too expensive. In Japan, I can't buy them 2 - 3 tablets at a time. I have to buy them in a box with 20 or so tablets. I don't easily get sick so by the time I need them again, they've already expired.
I don't ignore the signs and wait for it to get worse. What are the signs? A sore throat and running nose, nasal congestion and sneezing.
When these signs appear:
I gurgle salt dissolved in luke warm water.
I buy a pack of Vitamin C candy, sold at convenient stores. My favorite is the one with the yellow label with VC2000cc written on it. I finish a pack a day.
I drink water as much as I can (usually 3 glasses). After I urinate, I drink water again. I do this over and over. Before I go to bed, I drink some water, too. If I'm awakened by a full kidney before the cock starts to crow, I get up, take a leak, drink some water again and go back to bed.
Most of the time this "preventive measure" works. But, after a week, when I don't get better or if I have a fever, I start taking medicine and see a doctor asap.
For more info about common cold, check it in Wikipedia under the name: COLD (disease)