Fat is best lost by cardio exercise, exercising in general, eating healthy food, strictly limiting refined carbohydrates. Refined carbohydrates are a major cause of weight gain, obesity, and many health related diseases.
When you exercise (running, walking, riding a bike, lifting weights, playing sports, etc.) your body creates energy and burns fat to do so. Depending on what you do, different areas of fat will be lost. Any form of running or riding a bike are the most effective ways to lose fat.