1) Dont expect to lose the weight quickly. Weight can take years to put on so dont expect to lose it in a week or so. Consider weight loss is going to take you months (or even years if you are very overweight).
2) Dont go ON a diet, CHANGE your diet, for the rest of you life. Too many people go ON some sort of fancy diet and then as soon as they lose the weight they wanted they go back to eating "normally" and put it all back on again.
3) Dont tell everyone your are on a diet or they will all comment over and over again about it, just start your weight loss program quietly and then people will gradually note the weight loss.
4) Just eat sensibly. Cut out all "high fat" and "bad" food totally. No more chips, creamy curries, sweets, doughnuts, pork pies, chocolate, pasties and so on. Just eat "good" food.
5) Make sure there is plenty of fruit and other "good" snacks in the house (carrot sticks that sort of thing) if you fancy a nibble.
6) Dont go shopping when you are hungry and buy the "wrong" things. Go shopping after you have eaten.
7) Dont fall for the "buy one get one free" offers in supermarkets, These are nearly always "bad" things such as biscuits, crisps etc.
8) Do some MILD exercise. Dont join a gym and go mad straight away or you wont keep it up. Start by going for a short walk each evening (just round the block) and then gradually build it up over a period of weeks and months so in the end you will be able to a brisk walk of 2 or 3 miles.
9) Dont weigh yourself every day (once a week is enough) and dont get depressed if you dont lose weight in a week. Some weeks you lose more than others and with sensible eating the weight will come off over time.