If you can, try and cook from scratch as much as you can using fresh ingredients that have been processed as little as possible.
Eat 3 meals a day (something along the lines of a bowl of porridge or omlette for breakfast, a chicken wrap and greek yoghurt with fruit for lunch, a homemade chili con carne or fish with potatoes and veg for dinner then a small bowl of icecream or chocolate bar and things like fruit, dried fruit, nuts and seeds for snacks). Drink a lot of water. Keep active.
Healthy eating is quite simple!