Strength train 2-3 times a week
Nothing will help you lose body fat and get into shape fast like regular strength training. For best "fast fitness" results, do a full-body strength-training workout at least twice a week, using moderate to heavy weights. You'll burn calories, boost the metabolism, and build lean muscle quickly... all in one fell swoop!
Eat a 90% unprocessed diet
Get 90% of your weekly calories from healthy, unprocessed foods: meats, nuts, seeds, veggies, fruits, beans, legumes, potatoes, etc. Avoid grains, refined sugars, processed flours, and highly-refined fats/oils. 10% of your calories can come from 1 or 2 "cheat" meals where you eat pretty much anything you want, in order to reward yourself, help with exercise recovery, and confuse/stimulate your metabolism.
Eat starchy carbs and sugars infrequently
Carefully limiting your intake of "bad" carbohydrates is key to fast, natural fat loss. Avoid simple sugars and starches most of the time. Consume them only in your cheat meals and, if you're doing heavy strength training, after your weightlifting workouts. This will help you cut calories and stabilize your blood sugar and insulin levels.
Do smart cardio
You don't need to spend hours doing long, boring cardio workouts to burn fat quickly. Focus on smart, efficient cardio exercise: things like high-intensity interval training and taking part in fun sports and intense activities like hiking. View cardio as a "compliment" to your full-body strength training, not your primary form of fat-burning exercise.
Eat protein often
It's very easy to control hunger, limit food cravings, stabilize blood sugar and insulin levels, and keep energy levels high and stable: eat a small amount of protein every few hours during the day. This one diet "trick" is one of the best natural ways to lose fat fast and it works almost every time!