This is pretty much how I did it...
It's both very simple and really difficult at the same time. The real keys are brutal honesty with yourself and planning. The final bit is maintenance; the changes you make to lose weight must be sustainable as you will need to hang on to those changes to keep the weight off forever.
- Logging - very very very important that you brutally honestly log absolutely everything that passes your lips, having weighed it to be certain of how much you've had. That last couple of spoons of yogurt from the kids' dessert at dinner -does- count; that bite out of your best friend's hot-dog while you're out at the cinema -does- count; but it is -so- easy to forget that you had them, forget to log them and then wonder why the numbers seem to add up but the weight loss isn't happening. It is a well known phenomenon that people almost never log everything they eat, not because they want to lie or cheat, but because they actually do forget things because their brain doesn't see it as important at the time. So, if you're out and about and don't have access to your online logging resource (in my case Weight Loss Resources - WLR), keep a notebook, write things down and then enter them into WLR when you can. And weigh everything. Portion sizes do matter. Seriously, take a look here.
- Exercise - can make it harder to be sure of staying inside your allowance; the calorific value of food is a reasonable guess, based on burning food to see how much heat it gives off. Not exactly the same way your body processes it, but near enough for an estimate. The same is true for exercise; the effort required for two different people of the same size, weight, height and age may differ based on so many other factors. The estimates in WLR for exercise are quite variable and if you want to be closer to a more accurate estimate, invest in a heart rate monitor if you can. But -do- exercise as it will help to maintain your existing muscles while you're losing weight; it's no good losing lots of weight that's muscle as you won't get any definition in your shape and it's less "good" for you to be losing weight through muscle loss than fat loss.
- Snack. Regularly. Seriously. If you don't allow yourself to get hungry during the day, by eating little and often, you end up eating less overall to feel satisfied and lower the likelihood of splurging. Or to put it another way, if you leave it too long between meals you will most likely eat bigger portions and with less careful choice in those meals.
- Planning - Plan your food and exercise at least a day in advance, if not for the week. If you plan, it's harder to have little "oops" moments and you can plan in for treats to keep you from straying too far off the path or help you make informed choices when spontaneous things happen.
- Eat enough - It can be worth trying for a slower pace of weight loss as you may not be getting enough energy to keep your metabolism working properly. Many people have switched from 2 or 1.5lb loss rates to 1lb loss rate and suddenly the weight starts coming off properly. It varies a lot from person to person and giving it a go for a few weeks is really the only way to find out what will work for you.
- Have a "down" day/week every now and then. I was lucky that I never really needed to do this, but very many people find that their bodies are clever and cotton on to the fact that they're getting less food/more exercise and adjust your metabolism to deal with the reduced intake vs. output. Keeping your body guessing (but do stay on or under maintenance kcals) can help break out of that learning behaviour and kick your metabolism back to where it should be. If you're doing heavy exercise 3/4 times a week, maybe take a week off from it every 10-12 weeks. Or plan in a "cheat" day every week or fortnight where you do eat up to or even a bit over maintenance kcals rather than sticking to loss.
- Weigh everything. Unless you have the most amazingly accurate estimating skills, your portion sizes WILL drift. And usually upwards. It will start to add up to a few more kcals every day than you're logging and again you'll wonder why the kcals seem to add up but the weight loss isn't doing. In effect, you're kidding yourself. Stop it.
- Don't rely on the scales for the measure of success. Take body measurements periodically, maybe once a month, and keep track of that as well as weight. You may find there are times when the scales don't shift, but your body changes shape and you lose a few cm around bits of yourself.
- Patience - with yourself and with the people who will try to, knowingly or not, sabotage your hard work. You are only human; you will have off days and that's OK. Just as long as they're not every day ;o) And other people may not understand what you are trying to do, how or why and they can in a well-meaning way end up trying to sabotage your efforts by offering you food, tempting you out of exercise or saying "oh come on, you're not fat!". It's down to you how you deal with it; I wasn't very good at that part, to be honest, I just hid and didn't go out!
There -will- be hard times; I remember many many tantrums and fits of tears during my main weight loss period. The forums on WLR can really help with that and with advice and support when the going gets tough or you have questions.
So remember... plan, Log EVERYTHING and be honest with yourself. Losing weight isn't rocket science but it isn't easy either. You can do it. You will get there. But you have to really want to change your lifestyle and keep it changed for life.