building muscle

My training program says that if you can do 3 sets of 12 reps at a certain amount of weight with no resistance, or it's extremely easy to do those 3 reps of 12, then you need to increase the weight amount.

thanks- actually i?ve been doing 3 sets of 12 reps with 2 5lbs weights.....for upper body - for lower body i try lifting 15lbs in total. It?s really hard, but i like the challenge.