Remove the eyes from pineapples, and the fibrous core.
Split apples, cucumbers, watermelons, and similar fruits and vegetables, and remove their seeds and any stems.
Use seedless grapes, and make sure there are no stems lingering.
Peel bananas, avocados, oranges, and any other fruit or vegetable with a tough skin.
For citrus fruits, remove the pith (the white fibrous stuff) as well.