Always remember muscles are not made in the gym. Muscles are broken down in the gym and are made when you eat right and take enough rest.

When trying to build muscle it's important not to let your ego takeover. Don't be worrying who is watching you, so you try and lift heavier weights than you normally would. The quickest way to injury is lifting weights that are too heavy, which makes you lift with improper form.

I would say that you should spend no longer than 45 minutes in the gym and train every muscle no more than once a week.

One of the biggest mistakes beginners make is thinking the more they train the bigger they will get. Beginners never give their muscles enough time to recover so keeping their muscle gains to a minimum.

Personally i would rather give myself more time to recover than not enough time to recover, then at least you've got the full gains from your training session and you feel ready to go again for that particular muscle in the next workout.

If your going to the gym and your lifting the same weight as the last visit but you find that you've done 1 oor 2 reps less than the last time that usually means your overtraining and your muscle hasn't recovered 100%. You should be increasing your reps every time you go to the gym. Your reps should never decrease.

If you feel that you've given a particular muscle plenty of time to recover yet your weight and reps are remaining the same then you will have probably hit a "Plateau"

The best way to get out of a plateau is to change your rep range. Try using different weights so you can get your rep range between 4 - 12 reps. For example use a weight to go to failure in the 4 - 6 rep range one week. Then the next use a lighter weight to go to failure in the 10 - 12 rep range. The next week use a weight to go to failure in the 6 - 8 rep range. This way you are not letting your muscles become accustomed to what they will be lifting and should have you bursting out of that plateau in no time.

Remember it's not natural for your body to grow massive so if it can get away with just staying the same size it will. It's up to you to keep changing your rep range and your routines so your body stays in a constant state of growth. Applying these priciples will help you to gain muscle fast.