I have become obsessed with avoiding colds and have only had one mild one since then
however, this has involved being a tad anti-social - actually asking cold-ridden colleagues to step away from me and talk from there if possible!
I also clean my desk, computer, phone etc and even spray the door handles etc when people have colds - AFAIK cleaners don't do this every day so I do!
also I use a nasal spray preventative thing - cold defence - before getting on the Tube
Wash hands frequently and never touch face if possible!
Take allicin if I think I have a cold coming on
Before getting really neurotic about it, I'd have at least 3 a year and they would go on for a week. September 2016 is the last one i had and it was only a mild one that went on for 2 days.
The handwashing and not touching your face is the biggest thing I expect. But I live alone which helps!
I have asthma and have had pneumonia in the past so friends and family know if they have a cold they have to cancel plans with me.