Get your vitamins from food i.e. leafy greens, cruciferous vegetables (broccoli, cauliflower, rich orange or peachy coloured fruits, mango etc., berries
Go to the doctor at least once a year.
Drink lots of water.
Yoga, stretching, weight lifts to keep your bones strong.
Avoid processed foods full of sugar, fat, and salt, which come in many disguises.

And, now that I've said all of that "know it all" stuff, did I do that my whole life? lol, I should have.....and getting out in nature, very important to connect with all there is.
Wish I could tell that to myself when I was about 18 and on my own.