You have to eat right and train right. That's the advice you'll hear everywhere from everyone. But the reason for that is very simple and unknown by most of the people. Once you understand this and you get used to it, you'll success. When you were for example 160 pounds, you were training and eating for a 160 pounds person. Once you bulk up and you reach for example 190 pounds, you ate and trained for 190 pounds and now YOU HAVE TO KEEP EATING AND TRAINING FOR A 190 POUNDS BODY FOREVER. It is a whole change in your life. Most of the people do a cycle, eat and train like a bull but after cycle they say "OK I'm done, finally I'm big" and they start eating and training like before; so what happen?; our intelligent bodies return to their previous state cause they are not recieving the right nutrition and training to keep that deformation of the human body. It is just simple as comparing a tiger with a cat. A Tiger needs to eat let's say 4 pounds of meat per day while a cat needs maybe half a pound a day and that difference is because the tiger is trying to keep 300 pounds of muscle while the cat is keeping 15 pounds.
I'm sorry for the long explanation but now you got the clear answer to your question. And this is one of the main reasons why experts and pros will always tell you that AAS are not magic.