There is a certain routine you should follow while body building.You cannot just pump iron day in day out to build muscles. If you do not respect your body then your body will break down.
a) Are You Sleeping Enough?
This was the hardest for me to do, I had to wake up early in the morning for work and I never got enough sleep, instead of going to sleep early I wasted my time watching TV(sometimes until 2 in the morning). A lot of testosterone is released into your body when you are asleep, most of the growing is done when you are sleeping and getting less than enough of it will keep you frustrated. I kept hitting lots of plateaus because of this problem alone.
b) Lifting The Same Weights Week After Week?
I did this when I was 16, I would lift the same weight all the time and wonder why my muscles are not growing. Week after week would pass, I would keep lifting the same weight and while it did get easier every week I did not make any gains. Muscle building requires you to add about 5% to the weight that you are currently every week, if you are bench pressing 100 pounds this week, you must bench 105 pounds next week and you keep going higher as the weeks pass.
All bodybuilders come in different shapes and sizes, things that work for one bodybuilder may not work for the other. You always have to try something new, a new exercise, and a larger amount of sets maybe take more rest. Professional Bodybuilders are guys who know their bodies, they know how their bodies respond to every type of food they eat and every exercise they do because they tried everything, they wrote it down, they experimented with what their bodies responds to.
In order to know how to gain muscle as fast as you can you have to know what makes your muscles grow faster, you have to try new stuff to find out what works for you. I can tell you how many reps and sets I do each exercise but you will still need to adapt it for yourself because each one of us has a different body and what works for me may not work for you.
d) Stick To The Program
I used to be the type of guy who jumped from one program to another, while I already mentioned that you have to try new things I also need to mention that you need to be able to have patience. When I actually stuck to one program for 4 months instead of trying a new one every week I finally experienced some significant results, I gained 5 kg (about 10 lbs.), and I went from being 55 kg to 60kg (multiply it by 2.2 to get it in lbs.).
Learn to have the patience in order to get results because it will take you a very very long way.