Exercise as regularly as you can. Even if you have weeks where you don't feel like it or are recovering, if you exercise 2-3 times per week for an hour and stick to it as best you can, the rest should fall into place. It helps if you find something like love doing, so it doesn't feel like a chore (for me it is tennis or hiking). Cut out junk food and sweets as much as possible. Like whatever you're eating now, cut it to 10% of that, if even. Don't drink soda or other sugary drinks except on special occasions (try to keep yearly consumption at a maximum of like 10-25 L). Eat more fruit and vegetables. Consider walking somewhere instead of driving if it is only a few miles.
Also keep in mind your metabolism is going to drop significantly as you age without exercise, so you're going to need to start listening to your stomach and stop eating sooner. Honestly it absolutely sucks at first, but then you get used to it and you realize how miserable you were with all that sugar in your diet.