A lot of inexperienced bodybuilders, and even experienced ones, make the mistake of thinking most muscle growth takes place in the gym, and they proceed to pump iron like there's no tomorrow.
The problem is that after the workout, they go straight to the bar for pork chops and beer.
And then they wonder why they're not gaining muscle quickly enough! The thing with muscle growth is that it doesn't actually happen in the gym -- it happens when you're sleeping.
Sleep is the body's natural way to rest and repair itself, and this is when your worn and torn muscles form new tissue.
This is why it's extremely important to match your workout regimen with the proper nutrition.
Make sure you take in enough carbohydrates, protein, vitamins, and water.
This will make sure your body repairs your muscles at optimal rates while you're asleep.
The problem with some bodybuilders is that they think "more is better" when it comes to working out, so they push their bodies to their absolute limits in their exercise regimens -- even working out the same muscle groups on consecutive days.
This is obviously a bad idea -- if you don't give your muscles time to repair themselves, you might actually suffer muscle loss! The key to optimal muscle gain is to work out different muscle groups on different days.
This is to avoid overtraining any single muscle group during the week.
It's also a good idea to space your workouts with one rest day in between, so that your muscles keep growing at manageable rates.
To sum it all up, working out is only a small part of the equation.
You'll need to complete the package with the right nutrition and enough rest.
Stick to a sound routine and you'll be growing muscle at a pace your body is comfortable with.