Start by trimming off the top and bottoms then you want to cut across the eggplant making 1/2 inch rounds. Eggplant shrinks in size quite a bit when it is cooked so I always recommend cutting on the thicker side. You can also cut them lengthwise as well. Starting at the top and cutting all the way down to the bottom. Again 1/2 inch thick slices are ideal for eggplant parmesan.