If there is one muscle group that identifies you as someone who practices bodybuilding is the arms.  When someone asks you to flex a muscle, more than likely the muscle flexed will the biceps of the arms.  Isn't it true?

 

Thus, for many beginners who are just getting started, getting big arms is a huge priority.  Now, keep in mind that symmetry is a key and you don't want to have a situation where the only muscular part of your body is your arms.

Thus make sure that you place as much emphasis on every single other body part.With that said, there are two mistakes that are holding a lot of people from achieving the sort of arm growth that they could get:

Mistake #1: Sloppy Form

To get maximum stimulation on the arms you need to practice picture perfect form.  Breaking your exercise form will simply get others muscles involved taking valuable stimulation away from the arms.  Remember that the key to lifting weights is to use these as a tool to make the intended muscles work hard and grow as a result.  Sloppy form will not only risk a debilitating injury that can take you out of the gym for a long time, but also is robbing you away from your bodybuilding gains.

Mistake #2: Overtraining

Too much of a good thing can be bad.  Unless you have incredible genetics, or are a super advanced bodybuilder who knows what his body is capable of handling, 20 set biceps routines will just over-train you.  For the biceps and the triceps limit the number of sets to 6-12. The biceps is a relatively small muscle used in other movements for bigger muscles like the back and the shoulders. While the triceps is a bigger muscle than the biceps (twice a big actually), remember that it is used for all the pushing movements of your chest and shoulder exercises. Thus, there is no need to perform more than 6-12 sets either. If performing triceps after a chest workout 6 sets will suffice. If performed any other day you can do as much as 12 sets provided you have a good recovery capability.