Over the last 12 months I've been able to lose around 80lbs in body weight. For the most part this will have been from exercise, but I also eat reasonably well.
The following is one (very subjective) order of operations for improving your diet.
If it isn't good for you. Don't buy it.
If I have crappy food in my fridge I will always eat it. I know this because in every instance that I can think of that I've brought something that was bad for me home, I've eaten it in one sitting or the same day.
To satisfy my sweet-tooth cravings I buy low sugar/low fat yogurts and fruit. I like eating both and I eat only what I like the taste of. If I get bored of a type of fruit or brand, I try a different one.
Most cardio equipment at the gym will give you a rough indication of how many calories you've burned. If you enter your body weight, Strava can do the same. When you're conscious of the number of calories you can burn and the time and effort it requires to do so, you'll start to think more about how many you consume from food.
For example, I can burn 550 calories by running 5km. This might take me 25 minutes and if I try hard I'll want it to be over at the end. A side of fries will bring me close to this and the effort I've put in will have been cancelled out.
Pay attention to serving size.
Food packaging displays the fat, sugar and salt values for eating a certain quantity of food. Don't assume that a green label means something is empirically "healthy". Ensure that you're content with eating only the amount that the packaging states and if you do eat more, be mindful of how much fat, sugar and salt you're consuming in one day. E.g. a 1/2 pack of fresh pasta is 20% of my daily intake, so a whole pack is 40%.
If you want to eat rubbish food, go ahead.
It's human to crave something sweet or oily every so often. Suppressing those urges will only make the cravings worse. It's fine to eat unhealthy food once in a while as long as you moderate your intake. Assuming you're also exercising, you won't feel like eating crap all the time anyway.