Training arms can be the most enjoyable part of your workout, and it is easy to get motivated for arm training. The arm muscles are relatively small and recuperate quickly, however for these reasons it is easy to over train them. Some people have the genetics to gain arm size easily, but anyone can put inches on to their arms if they follow a few simple rules. There should always be a degree of variety to your arm workouts, if you did dumbbell curls and tricep press-downs last workout, hit them differently this time, with exercises you possibly don’t like doing.
You should always include an exercise that includes supination (hand rotation) in your bicep workouts, and include a compound movement when hitting triceps. The biceps respond best to high intensity training, not mammoth 1 hour sessions of low intensity, low variety training. Be sure to hit both heads of the muscle, and try to include at least 3 sets that hit the Brachialis muscle, which is a ball shaped muscle that pushes the biceps up nicely (check out Arnold’s upper arm for a prime example).
Triceps are heavily involved when bench pressing, so including a compound movement will not only add mass and muscle density, but will also help increase your bench. Try close grip presses and heavy extensions; just make sure you have a spotter. Remember that the triceps make up for 2/3 of the size of the upper arm, and don’t forget forearm work too. Not only do developed forearms look good, they also increase grip strength that helps with when working other muscle groups with heavy weights, such as back.
Try not to train arms for more than 40 mins, you should hit them quickly and hit them very hard. Do not rest for more than a minute unless you really need it, and don’t waste time walking about between exercises, keep the intensity. Try to switch between low reps and high reps (periodization.). In general, execute the movements as strict as possible, but now and then throw in some cheat curls for example, these can really make your arms massive.
As with every other muscle group, rest and recovery is of utmost important, you can not expect your muscles to grow if you are constantly training, and not giving them the proper fuel (see rest & nutrition).
Make sure you warm up and then stretch properly before any workout. Continue to flex and stretch between sets.
Include variety in your workouts, mix it up.
Include hand rotation in biceps routine.
Include compound exercise in triceps routine.
Plenty of rest and calories.