There are plenty of things you can do to keep your immune system strong so that you can avoid winter colds and flus.
1. Eat nutritious food. Okay so this doesn't only apply for winter, but if your are going to potentially be faced with more bacteria and viruses in winter then making sure your are ingesting as many nutrients as possible will help your body keep up with the requirements for strong defense.
Write something about yourself. No need to be fancy, just an overview.