Avoid smoking, alcohol, drugs and caffeine.
Wash your hands regularly and thoroughly. At least 15 seconds, with soap, also under your nails.
Try to express your emotions as much as possible. Contact others. Hug, cry and laugh together. The hormone 'serotonin' that you make then works for a higher resistance. According to research, singing also seems to unleash a range of good substances. False or pure, the immune system cannot make a distinction!
Take your rest. Excessive stress is one of the main causes of the development of diseases and aging. The moment you are stressed, all energy is lost to increase the alertness in the brain and muscles. There is then no place to maintain other bodily functions.
Get enough sleep. Preferably around 8 o'clock. As a result, infections get less chance.