Proper weight loss should be a lifestyle choice and not a quick fix, because with common calorie-restricted dieting, you'll only lose water and muscle tone, as well as mess with your metabolism. Therefore, as soon as you go back to your normal eating habits, the weight will creep back on -- and then some!
Motivation is key: visualise daily how you'll look in your party dress. Make sure you eat a proper, healthy balanced diet with lots of water, fresh fruit and vegetables. Also, you should cut down on refined carbs (white bread, white rice and white pasta) and white sugar, and completely cut any synthetic sugars from your diet (aspartame, nutrisweet). Make sure you do eat good fat (olive oil, nuts and seeds, butter), but ban the transfat (margarine, vegetable and rapeseed oil). And don't forget protein such as lean (skinned) chicken and fish.
As far as exercise goes, increase your daily activity by about 30 minutes a day. Brisk walking and performing bodyweight exercises around the home (such as lunges, tricep dips on a chair and planks while you're waiting for the kettle to boil) can be fit into your current schedule without too much effort.