1) Eat lots of fruits and vegetables
Citrus fruits such as oranges, lemons, limes and grapefruits have high concentrations of Vitamin C (your body doesn't store vitamin C so you need to consume some every day).
2) Do physical activity, exercise regularly
Going on walks. Do fitness classes, yoga, gardening, dancing and more.
Exercise moderately 5-6 days per week. Exercise helps produce more of the blood cells that attack bacterial invaders therefore leading to less colds and sore throats compared to people who don't exercise.
3) Sleep 7-9 hours a night
Getting 7-9 hours a night
Having a sleep schedule will help, try to turn off your screens 1 hour before sleep, and keep your bedroom as dark as possible when your going to sleep.
4) Don't smoke
Smoking cigarettes, vaping, etc. They contain so many chemicals and you don't want them in your body. Not to mention affecting your lungs and can cause fatal diseases such as pneumonia, emphysema, and lung cancer.
5) Laugh more
Laughter can boost your immune system as well as your mood.
Try laughter yoga
Watch a comedy
Joke around with your friends