What is the best diet and exercise for dropping weight quickly?

Eat less; move more. Anything that uses energy (calories) will help one lose weight, as long as he doesn't eat or drink back more calories right after the activity. Examples: if walking, take a longer route; use stairs instead of elevators; take multiple trips to and from the car when unloading groceries; park a block from school and walk there with the kids; at home, skip dessert and go walk around the block instead.
Moderation. The best meal plan is one that you will stick to, eating less, portion control and being active. If you take in 500 less calories a day, you should lose one pound a week which is a safe weight loss. I suggest a meal plan high in fresh fruits and vegetables since they are high in nutrients. Try to decrease processed foods as they are high in calories and low in nutrients and fiber.