Out of the three foods catagories, Protein, Starchy Carbohydrates, Fiberous Carbohydrates, protein is the food you should never skip during your meals. Protein is what keeps the muscles from eroding in your diet. It also adds energy and helps your metabolism to burn other carlories more efficiently. The key to eating protien is choosing lean foods. Beef, chicken, pork, eggs, nuts, and fish are all equally important in sustaining a well balanced diet. Fish especially has essentially omega 3 fatty acids which are very "good" fats to be include in your meals.
You must remember, we're counting calories here so it's important to proportion the amounts of foods correctly. Anywhere between 4-6 oz of lean meats or protein per meal is about right. Mix up your proteins at each meal. Some people will be able to include a higher percentage in their diets simple because of their metabolism composition. Some are able to burn one set of food calories better than others. On average the percentages maybe be 20% protein 40% Fiberous Carbs and 40% Starchy Carbs. You'll have to work and see what percentage works best for your body type. Staggering your calories each day is important to jump starting metabolism.
Overall, Protein is the main food you should consider eating before any others at meal time. Your body needs calories to burn and protein gives it the right amount of feul.