Stop drinking all soda and eating all processed sugar. Eat lots of fruits, vegetables, and meat. Track everything that goes into your mouth so you can keep the calories in a deficit. Beyond that, eat less - exercise more.
In my opinion the exercise is the most important long term because when you are in good condition you can burn a ton of calories everyday at a relatively low stress level to your body. That allows you to still eat a lot while restricting calories and losing weight. And once you reach your goal you can really eat a lot and not gain the weight back.
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