You are the only person with the exact hormonal balance and body chemistry that exists in your body. Use this to your advantage by getting to know your body and handling it the way it wants to be handled. There are 3 common areas where knowing your body will help you succeed.
Weight Training for Your Body
Many people want to follow the cookie-cutter approach to weight lifting. They want their routines handed to them. Instead, to be extremely successful, program your own workouts according to how your body responds. Not everyone responds well to high volume training. If you are one of those who doesn't respond as well to high volume training, change to High Intensity Training where the volume is lowered, but the intensity is increased. Do what is right for your body.
Eating for Your Body
Some people are extremely carb-sensitive while others are not. Some people do well with extremely high protein intake while others do not. You have to know your own body so that you can adjust your eating accordingly. This is the only way to assure success. Don't think that eating the same as the next guy is going to work for you.
Cardio for Your Body
Cardio exercise can be a controversial topic. I can tell you from personal experience that some people need a ton of cardio to stay lean while others can stay lean with a very low amount of cardio. This is a variable that you will need to understand for your body in order to get lean. I personally require a fairly high amount of cardio exercise. You may not. Do what is right for your body. Don't let the controversy over this topic scare you in one direction or another. You will definitely see great results if you do what is right for your body.