Well, different foods have different nutritional values, and you need a mix of different ones to get nutrition that's good for your body. Generally if you eat whole, unprocessed, brightly colored veggies and fruits, and eat lean meats like chicken and fish, you're doing well.
Eating food in moderation is important. Small portions. If you eat large portions your stomach will get bigger and bigger and you will eat more and more. Small portions will get u full quick. I eat whatever I want. I just eat very small amounts and I stay pretty skinny.