How hard you begin to train depends on your overall level of fitness. The soreness you experience can be lessened by decreasing the load you place on your muscles and by performing fewer sets. To avoid injury, you should gradually work into an exercise program and set the load to your individual fitness level. The load should increase as your fitness level increases.
Muscle soreness is common, especially when you first start exercising. If you are painfully sore for a long time, it may be time to change your program. Eventually, your muscle system will become accustomed to the stress and strain placed on it.