Pediatrician, medical educator, researcher, and author Aaron Carroll MD -- who somehow seems to have way more time than the rest of us -- talks about simple nutrition guidelines for healthy people:
You can read his New York Times article on the same subject here.
To summarize: He recommends that you prefer fresh food to processed and home cooking to eating out. Fat and salt aren't bad in moderation. Don't consume too many calories in liquid form. The conflicting nutritional advice reflects the difficulty of good nutritional research, plus the fact that many foods contain be contain both harmful and beneficial things. And of course people with food allergies and other reasons to restrict intake of specific things should pay attention to advice from their doctors.
Elsewhere (see for example this earlier post), Carroll has suggested that most people don't need nutritional supplements and pointed to the fact that in many cases supplements don't contain what they claim to do.