Don't smoke, eat healthy, take some supplements because they can't hurt (C,D,Zinc) have been shown to strengthen the immune system and most folks are deficient anyway. Get your affairs in order so if you become ill you don't have to pay bills or run errands (getting medication, etc), have some extra things that might come in handy like disinfectants (lysol, etc), food, etc, make sure all your chores are done so you don't have to deal with an illness and a mess at the same time. If you live with someone have a plan like a spare bedroom or something to quarantine in. Most importantly have someone you can speak with everyday so they can monitor your condition. If you become very ill and can't help yourself, you would want someone to be able to call the authorities to alert them to your emergency.
You could also order a quality thermometer, to help test yourself and anyone you live with, although it won't give results early enough to be reliable for avoiding contagion.