You cannot suddenly eliminate old habits. Nobody can. You need to take it slowly and surely.
If you were an ice cream, baked-goods, or candy addict--try just having less (like one a day, or one a week).
If it was snacks that did you in, try some different treats instead of totally eliminating snacking. Have an apple, or a clementine, or grapes.
If you just ate too much of everything, simply cut your portions by 1/3 or 1/2. Do not suddenly try to eat like a bird.
If you've never exercised, don’t expect to be an athlete overnight. Start by walking just 10 minutes a day, every day. You can build up over time.