Having managed to lose 3 1/2 stone since January I feel quite well qualified to comment here.
As some people have said, first and foremost is sort out your eating. For me this has been the key, yes I have added some exercise to my previously very sedentary lifestyle but the bulk of my weight lose has been down to sorting out my eating and my calorie intake.
I've done this simply by using myfitnesspal. It's free and a very simple way of keeping tabs on wheat you're eating, and before long it's second nature and you start to look at things in a different way as you start to see how many calories different foods have.
One example for you from my experience. Take Lindt Lindor, now before I started watching what I was eating, I could happily demolish however big a box of these was put in front of me, very easy to eat and delicious. Also 80 calories each, so polishing off 10 which I could do without a second thought would be 800 calories, or approximately half my calorie allowance for the whole day!!
My other recommendation would be to lose weight with other people if you can. At my work there are four of us who are working on our weight loss. We all get weighed in at the same time each week and are there to support and encourage each other, which has been hugely helpful. It's good to have some accountability as you want to be able to go to the weigh in feeling hopeful that you've done well and can share in that positive feeling with others. Also, it's great if you've had a bad week for whatever reason and there are people to support you if you're feeling a bit rubbish about it etc.
We all use myfitnesspal and have opened up our diaries and feeds to each other so we can see what we've al been eating and congratulate each other on a good day or when we've done a good amount of exercise etc.
My other advice would be to ensure you're drinking plenty, for me this has been a massive difference and has really helped fuel my weightloss!!
Good luck with it.