As with all new things, start with research. But remain wary of snake-oil claims. Anything which says it'll lose you more than 2lbs a week long-term is just there to take your cash.
Ultimately it boils down to:
- Eat fewer calories than you use.
- Exercise more.
Google yourself up a calorie use calculator to figure out roughly how many calories you currently use in a day. Then aim to eat about 500-800 fewer each day.
Build up to regular exercise. Go for walks, ride a bike, or even join a gym. Just about anything which gets the heart pumping and the sweat flowing is good stuff. Ideally you want to shoot for at least 30 minutes' exercise per day, preferably in a single instance, but if you're unable to manage that it's perfectly okay to build up to it.
Use this as an opportunity to switch to healthy eating. Fresh fruit and vegetables, fresh unprocessed meats and so on. Get to grips with the value of calories and you might be surprised or even horrified to find out how much is in what you've been eating, and it'll enable you to be more in control of your food choices, which helps overcome random cravings.
Don't have anything in the house that you wouldn't want to eat. Don't keep biscuits, chocolate, processed foods, burgers, frozen pizzas... If you wouldn't eat it to lose weight, don't have it at hand and don't buy it. Keep fruit and veg on hand if you're a snacker.
You need to get it straight in your mind that there is
no quick fix. It took you years to get to this size, and it
will take years to lose the weight again. Don't get disheartened if you "only" lose 1lb in a week - go find a 1lb weight and check out just how heavy it is. 1lb of human body fat stores 3,500 calories. "Only" losing 1lb means you've burned through 3,500 calories in a single week, and once you understand the value of calories you'll realise what a massive achievement that is. To help with motivation I suggest getting scales which can measure in fractions of a pound. Sometimes you may just lose 0.3lb, but scales which only measure in full lbs won't show your weight has moved.
You'll tend to lose a lot more in the first week or two of any weight-loss routine than you will once you've settled into it. Don't be disheartened when you "only" lose 2lbs in your third week after losing 6lbs in your first. It's perfectly natural, and 2lbs a week is a healthy rate.
Finally, do not weigh yourself more than once a week. Your weight fluctuates naturally throughout the day, and the best way to ensure you get an accurate picture of your weight loss is to weigh in weekly under as similar circumstances as you can manage. For example I weigh in at 8am every Saturday morning, after the morning wee but before breakfast. If one day I weigh in on a Saturday afternoon, I might've accumulated two meals and 1.5ltrs of water and not yet had a bowel movement, so the comparison will be next to irrelevant. You sweat a lot of fluid out overnight, you eat varying sizes of meals throughout each day, you might be having an upset stomach one day or be subject to any one of a hundred other minute fluctuations which together could add up to you panicking that you haven't magically lost 1lb overnight and so to console yourself you... go eat a cake, a Mars bar, and a zinger tower burger
Good luck!