In order to avoid harm and over-training, it is recommended to space your workouts by 24 hours. During these 24 hours your body repairs the muscle fibers which may have been damaged by micro traumas during your workout.
By allowing time for this recovery to occur, your body will adapt, and muscle fibers will build in strength and endurance. This is actually the best way to progressively expand your training. Otherwise your body could become strained, and thus be more subject to harm.
If you insist on training two (2) consecutive days, it is then recommended to vary your workout and it`s intensity. For example, if you did a workout to build and strengthen muscles one day, you may follow with cardio exercises the next day. Similarly, if you concentrated on upper body training instead, select lower body exercises the next day.
Have an enjoyable and "safe" workout!