One simple thing that can be done is to try and reduce as much stress in your life as possible. One of the negative side effects of stress is that it weakens your immunity. A form of meditation that is effective is to think about positive things, and this will reduce your stress levels. You can also exercise regularly, as this has also been known to lower stress levels. Both of these things, if done consistently, can make your life much less stressful, and keep your immune system strong and healthy.