I wrote this awhile ago, but it might help:
The trick to healthy eating is getting the junk out of your system. Right now you're craving things like sweets, chocolates, crisps and carbs because that's what you're body is used to. The first few weeks are always the hardest to get over but once your body starts running on a new fuel of healthier food it will be much easier and you'll find that your body craves natural sugars rather than synthetic ones.
I used to be in the forces reserves, and did a lot of physical training and I have to admit I'm not a fan of diets or fads. They are a quick fix solution that aren't very good for your body and you're likely to just put the weight back on once you stop. It's better to alter you approach and attitude to food first, then concentrate on the exercise. You'll also find when you start exercising that you crave healthy food that gives your body the energy it needs to complete tasks.
If you feel like you have the motivation to do it alone, then I would start by clearing out your cupboards and fridge. Get rid of any junk food, food high in saturated fats, sugars, synthetics, caffine, etc. Then go shopping. I find online shopping best as you stick to a list and aren't tempted by 'just one bag of crisps'. Fill your basket with naturally healthy food. Oatmeal, brown bread, brown rice, vegetables, etc. Use things like honey instead of sugar, natural yogurt instead of processed, fresh veg instead of frozen, sunflower and pumpkin seeds instead of crisps, etc.
Do this for two weeks without limiting what you eat, and without exercising. Doing too much at once is what causes most people to fail. By concentrating on JUST cutting out the rubbish from your diet and only eating healthy then you are more likely to succeed as you will only have one thing to concentrate on. You're also giving your body a chance to detox to get all the junk out of it first before starting exercise.
After two weeks you should notice that you have more energy (remember not to eat less/cut portions just eat healthy) and that you've lost your cravings for things like fizzy drinks and sweets. Your body has got used to natural flavours again.
Now you can start to exercise! You should also consult your doctor before doing any exercise if you haven't done any for awhile. Start by making sure you eat a healthy breakfast like oatmeal and honey which will give your body the fuel you need to exercise. When you're losing weight you should ALWAYS eat three healthy, balanced meals a day. NEVER scimp or go without. If you do, you're body will only store the fat from your next meal rather than burning it off as energy so you're actually tricking your body into retaining weight by not eating.
So start exercising by going for a 20 minute walk. You can find exercise plans on the internet, but you'd look at increasing this amount every couple of days at first by about 10 minutes. Remember to just walk, and do it every other day and rest at the weekend. The second week, walk for 10mins and jog for 2 minutes and repeat. Build it up slowly.
It will take you awhile, but by getting your eating habits sorted out first you are much more likely to lose the weight, be healthy and keep it off for good.
