Recently a variant of Reiter's default logic, called constrained default logic, has been developed in order to overcome certain short-comings of the original approach. In this paper, we introduce a very simple but powerful extension of constrained default logic, called preconstrained default logic. We demonstrate that adding certain preconstraints to default theories results in very expressive systems: Apart from representing heuristic control information, pre-constraints provide simple mechanisms for dealing with default lemmas and for incorporating priorities. Finally, we describe how pre-constrained default logic is related to other well-known approaches.