There are a number of different herbs and other natural products that can help.  But this is even simpler and more basic.  It's, simply, washing.
 
First, there's hand washing.  A person can wash their hands fairly often with anti-bacterial soap, since there are germs on many things that people touch.  It doesn't hurt to wash items that are frequently touched, either, like doorknobs, telephones, and keyboards.
 
Also, there's nose (nostril) washing.  Since many germs enter the body through breathing.  There's a new product out called the "Neti Pot" available at Rite Aid stores.  It uses plain salt water to rinse out the sinuses.  If that is too gross for some people, just a cotton tip dipped in salt water, used 2 or 3 times a day would do some good.
 
Stay healthy this winter, Doves!!!
 
Gloria