To "scribe" in a tile, you can cut the tile slightly oversize, and then place it in its fixed position making sure it is horizontal or plumb. Then run a pencil or whatever marker you use for the type of tile you are using along the ceiling. it will follow the profile of the ceiling leaving a mark on the tile for you to work to. I just run this along the wet cutter to take off the excess not required. You then dry fit the tile before fixing. It may be necessary to do this a couple of times to get it perfect but practice will make perfect a s they say.
