Have a regular workout
Physical exercises have a big impact on our bodies. Not only they improve our mood, increase energy, or help us build our dream body, but they make us more resistant to the infections! Oppositely of a common belief, the direct correlation between being more susceptible to infection straight after a workout has never been shown.
Although physical exercises increase your cortisol levels (so-called stress hormone, decreasing the immune response), once it comes back to a normal value it creates the opposite effect and improves both humoral and cellular immune response. It means that with each workout your immune system gets stronger.