I am not a medical professional. What you are about to read is based on my years of observing myself, learning from elder people, and reading.
To my understanding, the colds virus is already in our system but dormant. According to my own understanding, the colds symptom show up when our body resistance is down. So, the key thing to do is to keep your body resistance up. Things like taking Vitamin C, Multi-Vitamins, Exercise, Proper Diet, Enough Sleep, Enough water per day, etc. all help contribute to keep your body in good shape. Also, maintain a good standard of hygiene.
When I am down with the flu or colds, I get lots of sleep (rest) and drink (unsweetened) Pineapple Juice or Lemonaide (using fresh lemon juice). Yes, Vitamin C does not cure the colds. I found that enough rest/sleep and lots of water helps a lot. I just bombard my body with Vitamin C so in case my body resistance starts building up again (i.e. I start getting well), that extra Vitamin C in the system will help prop it up and get it going.
One thing I have noticed that brings about colds or the flu is when you let your core body temperature fall below normal for an extended period in time. A drop in core body temperature, in most cases (personal experience), makes those dormant viruses become active.
Phil