Here are the best principles for arm training:

1. MAIN OVERLOAD: To force a muscle to get bigger and stronger, you must continually overload it with heavier and heavier weights. So when you see your favorites doing barbell curls at 225 pounds or doing lying triceps pushdowns at nearly 300 pounds, you can understand how the overload principle builds massive arms. Remember, those bodybuilding greats took a long time to put on those pounds, but they kept adding weight to keep gaining muscle.
2. TRAP PRINCIPLE: Most bodybuilders train to failure with every set of their arm workouts, but the ones with the biggest arms invariably train past the normal point of failure. The easiest way to do this is to first take a set to failure, then use enough of a trap to propel the bar past sticking point, after which you slowly lower the weight back to the start. Two to three cheat reps at the end of a set are adequate to encourage gains.
3. PRINCIPLE OF FORCED REPRESENTATIONS: Forced reps give you a more accurate way than cheating to continue a set past failure. Simply have a training partner lift up evenly on the bar, with enough force to allow you to get past a sticking point and achieve two to three forced reps. You can maintain tighter form if your partner removes the right amount of stress than if you try to hit the reps just by cheating. The difference between the two techniques is that forced reps require you to have a training partner available.
4. PRINCIPLE OF DESCENDING SETS: This method, also called stripping, is similar to forced reps, but requires two training partners to remove the plates from the bar. Load the bar with lots of loose plates, but don’t lock the collars. Stand tall and do about six reps of strict or barbell pushups to failure. Your partners should then remove 10-15 pounds from each end of the bar to allow you two to three more reps, then remove additional weight for the final two to three reps. This principle was one of Arnold Schwarzenegger’s favorites.
5. MAIN REST-PAUSE: This is the fundamental principle for building mass and power in any muscle group, and you don’t need a training partner to use it. Set up a bar with a weight heavy enough to allow for only three or four strict repetitions of the barbell curl. Place the bar on a flat exercise bench, then lift it up and do as many strict reps as possible. On failure, place the bar back on the bench and take a 10-15 second rest pause to allow your biceps to partially recover. Raise the bar again and do as many reps as possible on strict form, which might be just two or three. Take another rest break, then force yourself one or two super intense final reps. With rest and pause training, you probably won’t need more than two or three sets for each arm muscle group.