Lorraine, are these 'sets' composed of a LH and a RH door that meet in the middle?
Are your hinges spring loaded or no-mortise?
Regardless of type, I use shim strips to center the doors in the opening and I try to install doors while the case is lying on it's back, if possible. The most difficult to install is the spring loaded type because the spring is fighting the door from being flush. So, the easirst way to get around that is to mount the hinge to the face frame first, mark the back of the door where the hinge mounts there, then open the door and hinge and use the marks to align the hinge.
However, if that's not possible, I use spacers (hot glue will keep them in place and the strips pop off when done) on the door top/bottom/mating edges. Attach the hinges to the doors, remount in the opening and have someone apply force to flatten the hinges. Use a self-centering bit, drill one hole in the middle, drive the screws. The doors should open and close stiffly. If so, pop off the shim stock. If the doors still open/close freely; drill & drive the rest of the screws.
Hopefully, someone who does this more than twice a year will offer a better solution.