How to gain an athletic physique:
Consistency. You need to consistently workout, and in your workouts you need to see consistent improvement. You need to get stronger, faster, gain more endurance, or do things more efficiently.
In your diet you need to find a way to keep yourself in a caloric deficit for weight loss and caloric surplus for weight/muscle gain while maintaining your lifestyle and the demands of your fitness and occupation.
That's it. Now, there are literally thousands of ways to do both of these aspects of physique development. The key is to find a way that you can be consistent with both.