Apples, pears and quinces may be sliced in one of two ways, depending on whether you want even crescents, or slices of exactly the same thickness.
For crescents: cut the fruit in quarters. With a small, sharp knife, cut each quarter lengthwise in even crescents. Cut toward you, following the shape of the crescent.
For slices: halve and core the fruit. Set the fruit cut-side down on a board. Cut in even vertical thick or thin slices.
The fruit half should hold together neatly after slicing. If you wish, flatten it to form a decoration of overlapping slices.