Hi Kendra! I try to eat foods in their most natural and unprocessed state (ie: eat an apple verses applesauce). I also limit the junk food (we all get craving for that now and then). I drink a good amount of water too.
Here is a post that I answered a while back pertaining to this topic that has a little bit more detail for you.
No I don't follow a book or principle. I just take it meal by meal. I open the fridge and pull out a protein, some greens, and some complex carbs and thats it. For instance, for lunch today I had 99% lean turkey burger, brown rice, steamed broccoli and green beans, and a glass of skim milk. I'm not one to make anything too complicated. Nutrition can get very complicated if you want it to be. I just am sure to eat a wide variety of healthy foods so that I get all the nutrients in me by weeks end. Hope that helps!
Take Care!