TAKE A MULTI-VITAMIN MULTI-MINERAL PILL EACH DAY

Do this no matter what else you do in your life. Start tomorrow. Go buy some if you don’t already have them.

No mega-doses, just one that lists most things at 100% (some will be less). Mega-doses of vitamins end up screwing up the balance in your body and prevent other vitamins / minerals from being absorbed and used properly.

Take it with a meal if possible. It's easier on the stomach lining, and things will be absorbed better if there's other food present.

Make sure you are getting some fat or oil with the meal – "fat-soluble" vitamins (A, D, E) must be dissolved in oil to get "passed on" to the body – otherwise they just go right through.

If your meal contains no fat or oil, a teaspoon of any vegetable oil will work. I use canola oil, but corn oil, olive oil, and many others will do the job.