As a general rule you need 3 portions of carbohydrate, (ideally wholegrains such as brown rice or wholewheat pasta), 3 of protein (such as eggs or beans), 3 of fats (for example a small handful of nuts or some avocado), 2 of dairy (like cheese) and at least 5 of fruit and vegetables. Drink lots of water and aim for about 1500 calories a day.
Avoid foods such as chocolate, cakes, fatty meat and creamy sauces. I wouldn't completely rule out any specific food though as this'll make you crave them even more. If you really like something naughty, try to limit yourself to once a week.
In terms of excersize, something as simple as an hours walk a day will vastly improve your fitness. Add in some weights a couple of times a week to build muscle tone.
Good luck. X