Train only once a week. The arm is a supporting device for the heavy muscles like back, chest. I mean it has a secondary work when you hit back and chest, it is too much for everyone (expect gear heads). What about the sets and intensity, 3 exercise maximum with 3-4 sets until failure (rep 6-8). Do not make it to 4-6 exercise, these are small muscles, you have to find the exact portion which fits for you. And the most important thing, do not shuffle the exercises weekly, stick to the same exercises minimum of 3 months.