These are the best principles for arm training:

1. MAIN OVERLOAD: To force a muscle to get bigger and stronger, you have to continually overload it with heavier and heavier weights. So when you see your favorites doing barbell curls with 225 pounds or doing lying triceps extensions with 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 in their arm workouts, but those 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 trap enough to propel the bar past the sticking point, after which you slowly lower the weight back to the start. Two or 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 precise way than cheating to continue a set beyond failure. Simply have a training partner stand up balanced on the bar, with enough force to allow you to pass a sticking point and achieve two or three forced reps. You can maintain tighter form if your partner removes the right amount of stress than if you try to do the reps by just 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 block the collars. Stand tall and do about six strict reps or barbell push-ups to failure. Your partners should then remove 10-15 pounds from each end of the bar to allow you two or three more reps, then remove additional weight for the final two or three reps. This principle was one of the favorites of Arnold Schwarzenegger.
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 barbell with a weight heavy enough to allow only three to four strict barbell curl reps. Place the barbell on a flat exercise bench, then raise it up and do as many strict reps as possible. Upon 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 strictly as possible, maybe just two or three. Take another rest break, then force 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.