RMS80's advise is great. Zicam is very good too.
Personally, I use a few things when i get, or feel I'm getting a cold.
1. Real mexican food with lots of HOT salsa and chili. I love my local taco cart. The spicy food drains and clears my sinuses completely and, i kid you not, almost always makes me cough up phlem from my lungs wether I'm sick or not. The onions, tomatoes, cilantro, jalapenos and other chilis are PACKED with super healthy vitamins and phytochemicals. A couple of meals like that usually wipe it out for me. Your bowels may regret it in the morning, but it is highly worth it IMHO. Just take some pepto or antacid.
2. Supplement with extra GSE and GTE w/ Forskolin, ginseng and vitamine D and C. Also, an extra Gut Health pro biotic and Zinc.
3. Make sure I eat enough protein and carbs, but no simple sugar stuff or junk food.
4. Make some tea out of the juice of a few lemons, honey, and ginger. Honey helps coat the throat real well and gets the ginger and lemon to really destroy the little germs. Also use traditional teas like peppermint, licorice, ginseng and green tea. Using the teas is kinda last resort for me though just because I'm lazy.
These usually work for me. I hate going to the doctor when I'm sick, but sometimes I just have to do it. These 4 things I've picked up over the years have stopped colds in their tracks even when I was sure I would have to go to the doc the next day.
However, it's better to go to the doc if it gets real nasty and won't let up despite these sorts of home remedies. One reason to consider in particular is that some bacteria (think strep or similar) when left untreated can make its way to the heart and do irreparable damage to it. Not worth saving the 20-30 dollar co-pay to not go and get anti biotics.