Whole fruit has more fiber and less sugar. A cup of dry beans or two tablespoons of peanut butter can be substituted for a serving of meat. You can eat some sweets after you've met your requirements in the above food groups. Choose wisely, though. Eating half of a candy bar or a small bag of chips a day is fine, but you shouldn't exceed this on a regular basis.
Moderation is the key.
Of course, on some days you will overeat or not fulfill your food requirements, but strive to meet these requirements at least two out of three days.