Ceramic side down, so that it rides on surface of the rubber seal.
When installing the ceramic/rubber ring, the rubber will have a tendency to not stay in place, and separate from the ceramic. Use a metal washer to push down on the rubber. This applies even pressure to the rubber, keeping it in place, between the shaft and ceramic.
Do you have any metal washers with the kit? They are used to set the correct height of the spin tub. I am assuming there is a notch in the shaft, which must line up with opening in the agitator mount.
If you need images of this, I could check my service manuals, and scan it in.