Hello there!
There are different ways we can decrease the chance of catching the flu or cold.
1) Get vaccinated
Of course not everybody likes getting some shots next to their butt or their arms. But it worth it! After couple minutes, the little pain will be gone.
2) Exercise
Honestly, this is one of my favorite :)
There are different kind of exercise. Choose whatever you like to do. Personally, I prefer to run, go to the gym where they have the equipment.
3) Drink enough water
When we are sick, like having the flu or cold, we are losing a lot of energy without recognize that. So one of the easiest thing you can do is drink water.
4) Take care of your toothbrush
Some people just don't care where they are putting their toothbrush. But the flu or the cold is like a virus that is spreading in the air. So if it is in the toothbrush, then later you used that toothbrush to brush your teeth, you'll get the virus.
As a future Surgeon, I know a lot about these stuff. So I hope this answer helps :)
As always, it is my pleasure to help students like you!