Not every biceps movement was done for 6-8 reps. Arnold identified certain exercises that he called "definition-building movements," which he performed with relatively lighter weights for sets of 8-12 reps. Here, his focus was on squeezing and contracting the muscle, and holding the peak contraction for a long count. Concentration curls, preacher curls, and alternating dumbbell curls were among his favorites.
Listen to your body. If you have a training day scheduled on paper but feel like rubbish, a day off focused on quality nutrition and adequate rest might actually improve your results. After all, you damage muscle in the gym; you build it with quality rest and nutrition. Pushing through when you're overly tired can be a recipe for disaster or injury. 

Develop your strength training routine. The exercises you perform will depend on your goals for your body and your stage in the training process. It's generally suggested, though, that you stick to the same major compound movements that most bodybuilders use, making this the cornerstone of your strength training. Later you can incorporate isolation exercises and machines into your routine, but right now you should be focused on leaning up and gaining muscle, doing the following exercises:
Other bodybuilders, such as Casey Viator and Mike Mentzer, used less sets in order to get more recuperation. They would limit the number of sets per exercise to only 3 and would also do less exercises to train each muscle group. This would bring their total number of sets down to 10-12, about half of what the high volume trainers would use. Mentzer was often quoted as only doing a total of 5 sets per muscle group.
If you follow a full-body program built around these seven categories, you'll be amazed at how well your body responds. If your goal is to add mass, these are the movements that will allow you to use the most weight and provide the training stimulus the body will need to grow. If your goal is fat loss, these are the movements that will allow you to burn the most calories and continue working harder in the gym. If your goal is just to get stronger and more athletic for whatever you decide to do later, these movements are the perfect tools.
Lindsay Cappotelli ensures she's consistently making progress by simply tracking her workouts online or in a training journal. "I like to log the exercises I performed, the weight lifted, the reps done, and the rest I've taken between sets, so I always know where I stand," she explains. "Since muscles growth is a constant challenge, I'll mix up my workouts by adding more weight, decreasing the rest between sets, or adding an additional rep or two."
After session 12, consider whether you need to increase the weight for any particular exercise. If you can comfortably do more than the RM of 12 exercises, increase the weight by a modest amount, say two pounds or a kilogram for isolation exercise muscles such as triceps and biceps, and 5 pounds or 2.5.kilograms for compound and large muscle group exercises like squats and deadlifts. When using dumbbells, this would apply to each one. Don’t increase the number of sets beyond 3 at this time.