I hate it when I get a cold!  As soon as I get the sniffles I take Vitamin C to fight it.
That's a good idea. There is some evidence that regular use may shorten how long a cold lasts.
I just take whatever amount is in a vitamin.  How much should you take?
You might want to read that bottle. I'm not exactly sure of the correct dosage, but too much may cause stomach discomfort, headaches, trouble sleeping and skin flushing.
What else can I take to prevent the common cold?
Best evidence currently out there shows the best prevention to be handwashing.
How frequently should I wash my hands?
Wash your hands every time you use the bathroom, before you eat and I also wash my hands after I've been in public anywhere to prevent and help minimize spreading disease
Which diseases can spread if you don't wash your hands?
Any bacteria or viruses could be spread, like the flu for example. There are so many illnesses out there that you have to watch out for.