Eat organic whenever possible. Make it possible. Preferably from grass-fed ruminants, natural-diet poultry, home-grown or farmers market vegetables and fruit. it's far more nutritious, and therefore one doesn't need to eat as much to be full, and not just full but nourished. Also, avoid GMO's as much as possible.
I beg of you though, do not go vegetarian or vegan. It's really not healthy for you. One of my favorite books is called The Vegetarian Myth. It's written by a woman who was a vegan for over 20 years, did everything "right" and wrecked her body in the process. It's scientific, with proofs and reasons, and it's readable. Along with that plea comes this: avoid everything soy. The book also explains why. Even if you don't believe me an are vegan or vegetarian... Read it so you know what the opposition is saying.
Learn to cook. Cooking does not mean grabbing a box from the freezer, taking a package out, removing the plastic, and heating it in the microwave. In fact, people should just get rid of their microwaves altogether. Really, it's healthier. Besides, not having one forces creative cooking: if it's there, it's far too easy to use it.
Buy a slow cooker and a nice toaster oven - you can probably get one for under $10 at your local second-hand store. Get some good, non-Teflon cookware, preferably glass (don't use put the heat any higher than medium for glass!), or coated cast iron. A crockpot is an essential. Buy the Nourishing Traditions cookbook.