I see A LOT of common mistakes people are making when 'dieting', and it's not something insignificant. If you think it's insignificant, it probably isnt. Let me help you by pointing out some of these..
Beverages: These are something that's taken for granted, you can get a lot of liquid calories. It has no nutritional, even if you drink 2000 calories, you'll still feel hungry, and then over-eat. You should always take note of what you are drinking, as this can be pretty big. Just say no sweetened soda and other drinks like latte, frappe, frozen coffee, smoothies or sweetened tea. Juice doesn't seem like a big deal, but eating the whole fruit would be far more benefitial, it would be more filling, it would have more fibers and few calories.
Skipping meals: Sounds logical, right? You want to lose weight, so you eat less calories = skipping some meals. That's a big NO. By skipping meals you're doing way more harm than good to yourself. Breakfast is the most skipped meal of the day, and it can be the most important one in your diet. Do not skip breakfast. If you're always running out of time, go to sleep earlier, you need more sleep anyways.
Giving into friends: You go to a restaurant, or come over at a friends house.. And there it is, a big bucket of ice cream, or pleasantly smelling hot pizza, your friend starts eating, looking at you weirdly as to why you're not taking a piece, you then-- WAKE UP! You have your own head on your body, you have to think for yourself, if anyone is insisting on you eating something, you have to nicely apologise and say you can't. You shouldn't lie saying you don't like that flavour, because you'd be tricking yourself too, you need to stay strong.
Forgetting your meal schedule: I see people forgetting when they have to eat all the time, if you do too, you should set an alarm to go off every two and a half hours, every day. This will not only remind you, it will also help you remember it better on your own since you'll be looking at the exact times every time it goes off. The good thing is this can be done on almost any phone.
Not drinking enough water: I can't stress how important water is, see this.
Weighting yourself too often: People are getting more and more obsessed about the scale, media doesn't really help with this fact. The thing about weighing yourself is that your weight changes constantly, in the morning you'll be one way, in the evening you might be shocked, how could you have lost/gained so much in one day?! Only to be let down the next morning.. What you have to do is weigh yourself daily, taking notes of your weight, then taking the average at the end of the week. You'll know your exact weight then.
Forgetting this is a lifestyle: If you think dieting is just a two-week thing which you have to last through, and then you're done - you're just plain wrong, it can be, but you're going to go back to the same weight you were before the diet, possibly even more since now you're 'allowed' to eat anything you want. What you have to realise is this can be a lifestyle, you can be healthy, fit, strong and flexible your whole life, you just have to make it you, and let it make you.