I think the most important thing is to develop good form. The next most important thing is to shoot a lot of quality shots. Underlying both is maintaining a high level of interest and enthusiasm, so you will shoot every day, if possible, because you want to.
Given that list of priorities, my advice is to do what you feel like doing. If you feel like shooting all your shots at 20 yards, or 5 yards, do that. If you feel like mixing up the distances, do that. I think you will progress further that way than by sticking to a preconceived plan.