Preparatory actions are done before doing something else as a form of preparation or as an introduction. At least a year's preparatory work will be necessary before building can start. = preliminary
of or pertaining to preparation, having the purpose of making something or someone ready, preparative
If one action is done preparatory to another, it is done before the other action, usually as preparation for it. Sloan cleared his throat preparatory to speaking
Preparing the way for anything by previous measures of adaptation; antecedent and adapted to what follows; introductory; preparative; as, a preparatory school; a preparatory condition