I've never been overweight, so I can't tell you much about losing weight. But I have maintained the same weight, shape and fitness level since college, so I know a lot about maintaining a healthy lifestyle. The main thing is consistency in diet and exercise. Don't work out so hard that you hurt yourself and can't exercise; and don't go on such an extreme diet that you can't maintain it. A consistent B minus in diet and exercise is better than bouncing between A plus and F.
Also, it's proven that willpower is similar to a muscle. If you try and change a bunch of habits all at once, you're almost guaranteed to fail. But like a muscle, the more you exercise willpower the stronger it gets. I'd start with reducing/eliminating processed foods and some light exercise, such as walking daily and going to the gym a couple of times a week. Figure out what works for you and build your healthy habits from there.
As far as your diet goes, whatever works for you works for you. I think most legit diets advocate eliminating processed foods, refined carbs and added sugar. I try and maintain a balanced diet and eat as much whole foods as possible. For exercise, whatever you enjoy doing and keeps you injury free is good. I bounce between high intensity interval training, yoga, cycling, swimming and going to the gym.
Most importantly, look at the next few months as building a foundation for the rest of your life. Don't worry about results. Establish healthy habits. Find what works for you. The worst things you can do is set unrealistic expectations and burn yourself out, or put all your effort into meeting your goals and then fall off as soon as those goals have been met.