Just eat real food. (JERF) Grass fed and wild caught meat, vegetables, fruit, nuts, and healthy fat. No processed foods, sugar, gluten/grains, dairy or legumes (beans including soy). Eat when you're hungry, eat till you're full. Higher fat and protein than carbs, if you want to lose weight. Higher carbs with endurance activity.
Getting started? Start with Robb Wolf's page and read his book: The Paleo Solution. Reading that book convinced me to try Paleo for 30 days and test out the science of it (he is a Biochemist). 30 days later, I was 100% convinced, have never returned to either the standard American Diet or "Boulder Healthy" diet (ie mostly vegetarian).