How do you know the proper rear brake adjustment on a 1987 Oldsmobile Cutlass Supreme?

Assuming it is rear DRUM brakes, adjust the shoe until there is friction when spinning the wheel or drum, back off a shade.

Most have self ajusters on them. Ajust them out until the drum will hardly fit back on. After you put the wheels back on and your done with putting the brake shoes on. Find a place where you can run your car in reverse safely. Go bakwards about 25 miles an hour and hit the brakes hard. Do this several times and they should ajust themselves out to where they should be. This is assuming like above we are talking about the back brakes and they are drum style brakes.