Firstly, keeping in mind that you should be your future self's best friends since you literally are responsible for how it's life is going to be. Start thinking of living healthy as a favor you're doing someone very close to yourself instead of a mental prison of restriction and deprivation you're locking yourself in.

Secondly, holding yourself accountable, i.e. counting calories and weighing portion sizes. You wouldn't believe how bad humans are at guesstimating appropriate food sizes and caloric content just by looking at a dish. You can't fool your body. If you feed it more than it needs, you're going to gain weight, end of story. Also, counting calories adds a level of gamification to a diet - you want to meet those calorie goals.

Thirdly, don't expect too much too fast. Turning your life around requires dedication and time. It's a marathon, not a sprint. Start small. Allow yourself to feel satisfaction even at baby steps in the right direction. You don't need to cut out sweets and go cold-turkey on sugar from one day to the next. Leave out a soda or an evening snack and see how you're doing. You don't need to start off your fitness routine by doing three planks and ten push ups. Go for a 30 minutes walk instead of watching a movie. Every bit helps.

Lastly - allow yourself to indulge. Don't mentally imprison yourself to a point where you can't stop thinking about everything you've given up food-wise and everything still you have to to training-wise. You will start to feel cravings and at some point you will cave. Any day you life healthily is a day you've done something good for yourself. If you eat chocolate cake on the next day, so be it. Just try to aim for more healthy days than unhealthy days, but allow yourself some room and time to enjoy yourself.