Do some research on the Mediterranean Diet. It's one of the best, all around diets out there. Here's one website you can check out:
http://oldwayspt.org/resources/heritage-pyramids/mediterranean-pyramid/overview
Basically, one needs 4-5 servings of veggies every day, 1-3 servings fruit, about 5 oz lean protein (in the form of chicken, fish, red meats, etc), 2-3 servings dairy, along whole grains, nuts, seeds, beans and healthy fats. You can learn to judge your servings... for instance a serving of meat is about the size of a deck of playing cards. A serving of rice is about the size of a fist. There are also web sites you can go to, to find this information.
As benjysmomma said, be sure to check the labels of all packaged foods to see the serving sizes, how many servings are in the package and how many calories in each serving. For instance, if you eat a packaged dinner that makes 4 servings at 400 calories/each and you eat them all in one sitting, you just ate your entire calorie budget in one meal. Too often, we eat an entire package of something, not even thinking that just because it's a single package, doesn't mean it's single serving. I tend to do this with chips, pretzels, etc. Much better to split them into individual servings -- better yet, don't buy them...lol
Another thing to watch out for is sodium. Most pre-packaged products, including canned veggies, etc have way too much sodium for most of us. Too much sodium can cause fluid retention, which can make weight fluctuate by 3-5 pounds/day. High sodium use, fluid retention and being over weight have all been linked to heart disease.
Of course, also look at sugar content. Added sugar means more calories. Fruits should be limited to 1-2 servings/day, because of the sugar content and always opt for whole fruit over juices, since whole fruit has the benefit of fiber in the pulp, which helps slow down the absorption of the sugar.
Basically, fresh/frozen veggies, either raw or cooked are "free" when it comes to calories, unless you load them with dips or sauces, so you can pretty much eat all you want of those without going over calorie budget. You can jazz up cooked veggies with lemon juice, vinegar, whatever herbs and spices you like, as well as drizzle of olive oil. Try snacking on raw baby carrots and celery sticks, with 2 tbsp peanut butter... you can have all carrots and celery sticks you want and the peanut butter gives you protein and healthy fat. An apple and peanut butter is also good. Apples do have a lot of sugar, but again, that fiber helps keep the sugar from entering the blood stream too quickly.
I agree that buying chicken and fish (or other meats) in bulk, on sale and repackaging them into individual servings (or meals), will save you money and time. Or you can cook meals ahead and freeze them for quick reheating.
When on a diet like That you need to look on the bavk ofeverything at the serving sizes. Portions is everything I just recently started on a 1200 calorie diet and it really isnt as bad as you would think. Make sure you eat protein like chicken preferably grilled or baked less fat but keep an eye on your portions we buy from walmart you can buy chicken fish like tilapia and each piece is one serving at 100 calories stock up on veggies also one serving of carrots or broccoli is only 25-40 calories hope this helps some! (Also try and stay clear of breads a little is good but a lot of carbs they have 100% wheat and 35 calorie sliced bread)