One of the most common and important tasks in wave optics simulation is choosing what mesh spacings and mesh dimensions to use for a given problem. To obtain correct results, it is crucial that the mesh spacings are sufficiently small and the mesh dimensions sufficiently large, but if one makes the spacings too small, or the dimensions too large, that can greatly increase the simulation run time, and that may be unaffordable. It is therefore important to understand exactly what the applicable constraints are, so that one may choose mesh spacings and dimensions that will yield correct results without being over-conservative. However this problem can be nontrivial, especially when modeling propagation through aberrating media, or when there is potentially useful a priori information available which might allow us to relax the modeling constraints. For example, if the light source is known to be well-collimated, we know that all of the light to be modeled will be concentrated along one axis, allowing us to use smaller meshes than we would if the light were uncollimated. Similarly, if the receiver has a limited field of view, we need not model any light incident upon it from angles outside its field of view. In this paper we present a simple general method to determine what mesh spacings and dimensions will work for any given wave optics propagation problem, including problems involving propagation through aberrating media and/or a priori information about the source and/or receiver.