Write in a journal about your food consumption and notice a pattern. Do you tend to eat when you're happy? When you're sad? When you're bored? Do you tend to eat too much meat? Drink too much soda? Do you maybe prefer fast food because fresh food takes too long to prepare? etc.
Once you know what you're doing wrong, it'll be much easier to correct it and make some progress. Of course, regular exercise is also a must. Start walking for 30 minutes at least 4 days a week, and increase the duration and the frequency as you go.
