Observe your daily habits . . . wash your hands regularly and often, don't touch your eyes, etc. Be extra mindful.
Also, eat foods every day that strengthen the immune system such as onions, garlic and spinach.
Take B-complex in addition to a good multi-vitamin.
Strength training has been shown to strengthen the immune system.
Get extra sleep. Most people are sleep deprived. If your body is fighting a cold AND you follow a heavy workout program your body may need closer to 10 hours of sleep every night. If you want to live a healthier life it is worth considering the investment of sleep time. You'll have more energy, be more efficient, feel better, work better.