This is a simple concept that many healthy people have been following without realizing that they are doing it. The problem is that many unhealthy people don't listen to their own body and end up ultimately messing up their body's internal chemistry and rhythms.
Pay attention to what your body is saying and you will discover the best strategy for your dietary goals.
Rule #1. Eat when you are hungry (but not starving!)
It's not as simple as it sounds. Most people eat based on time of the day (breakfast, lunch, dinner), not when their body actually feels hungry. Sometimes people eat when they're not even hungry simply because it is "lunch time" or they will be starving at dinner/supper time because they were waiting since 3 PM to eat.
Also remember that sometimes thirst is mistaken for hunger. If you only ate one hour ago and feel hungry, drink a glass of water, wait 30 minutes and re-assess the need for food.
Rule #2. Stick to Smaller Meals and Snacks if your goal is Weight Loss
The question "How much should I eat" is often mentioned by dieters, and the amount is hard to ballpark. Different people have different needs based on their exercise levels and height. If you eat small meals and healthy snacks that are between 200 to 400 calories you will feel content, eating a total of roughly 1600 to 2000 calories per day depending on your size. If you're finding it's not enough or you're hungry again in an hour, raise the food intake by 100 calories until the adjustment works for you.
Try the following routine:
Breakfast 400 calories.
Mid-Morning snack 150 calories.
Lunch 400 calories.
Afternoon snack 150 calories.
Supper 400 calories.
Evening snack 100 calories.
Total: 1600 calories.
The exact times should vary day by day and be based on whether you actually feel hungry or not.
Rule #3. Eat Healthy
As often as possible try to stick to food that is not processed, fried, frozen or high in saturated fat. Instead, eat whole grains, dairy, lean meats, fruits, vegetables, beans, legumes, and healthy fats. Fruits, grapes, berries, nuts are awesome!
This doesn't mean you can't sometime indulge in ice cream or even bacon, but you should watch your calories when eating such foods.
Rule #4. Learn to Read Labels
Pay attention to labels on food packaging. Learn the differences between saturated (bad) and unsaturated (good) fats. Learn how many calories is in your favourite foods and drinks. Keep a journal of what you eat for a whole week once per month (don't do it constantly, its better not to obsess about it too much) and with time you will be able to count calories in your head without thinking about it. You can also get gadgets or Apps for your SmartPhone that can calculate calories for you. (eg. A nutritional scale for your kitchen can be quite useful.)
Try these 4 rules together and in combination with regular balanced exercise and you will see results.