As has been said, dont look for a quick weight loss.
It can take years to put on weight so dont think you can lose it quickly. Think about it in long term rather than losing it in a few week or months.
Also remember that we are ALL on diets, just some of us are on bad ones (ie we eat the wrong food).
So dont talk about "going on a diet" talk about "changing your diet".
Change your diet for the long term (or for the rest of your life) not just to lose the weight.
Cut out "obvious" bad things - chips, creamy curries, fried food, crisps, pork pies, sausage rolls, biscuits, cakes etc - anything high in fat or with pastry. Dont even have them in the house.
Many "packaged" items in supermakets like biscuits or pre cooked meals are often high in fat and suger and made with cheap fats so steer clear of them.
Have plenty of fruit and vegetables in the house. If hungry chew on a carrot or have an apple.
Do some moderate exercise. Dont go mad and join a gym, you wont keep it up. Just walk round the block each day, maybe walking further and further as you get fitter.
It CAN be done, but dont expect to lose 5 or 6 pounds a week, if you lose 1 pound a week, but every week, then eventually the weight will come off.
And dont get depressed if one week you dont lose any weight. As long as you stick to the "right" diet the weight will come off.