The biggest mistake that people make when trying to lose weight is eating very little or not often enough. You need to eat FREQUENTLY. I'm going to assume you're exercising. Even 2-3x per week helps greatly.
Eat moderate size, high protein meals, FIVE times per day. This seems like a lot? Think of it this way. When you eat just twice per day, what does that say to your body? You're body says "i'm not getting food often, so when i do, i need to make sure I store this in case I go a long time without food", so you start to STORE it AS FAT. When eat frequently, this speeds up your metabolism, and your body basically says "well i'm getting food often, so no need to store it.
Protein is important because it has a high THERMAL EFFECT. This means it basically generates heat when it is burnt off. If i remember...protein has a thermic effect of around 30%, carbs around 2-5%, fats like 0%.
Lean chicken (non breaded, skinless, no sugary marinades, no BBQ sauce etc.), 90/10 or leaner ground beef, tuna, eggs, vegetables, fruits.
Want to know a secret? Ground beef that says 80% protein/ 20% fat has about twice as much FAT as it does protein. This is largely because each gram of fat contains 9 grams, while carbs and protein have 4 calories per gram. If you don't believe me, check the label. It will say something like "254 calories" total, "Calories from Fat: 180". I believe it's 20% fat by weight, but that does NOT correspond to nutrition.
Green VEGGIES. You can eat these all day long and you will NEVER get fat.
Sugar is your biggest enemy. BBQ sauce, Ketchup, fruit juice, cut that out. White bread is also treated by your body almost exactly the same as sugar is.
Cut out the sauces and stick to spices. Sauces (ketchup, BBQ, whatever) are usually primarily comprised of one of two things for flavor: Sugar OR salt. use pepper, garlic, hot pepper, whatever you like