Clean fruits and vegetables with running water. Scrub firm products, such as potatoes, with a vegetable brush to remove dirt and contaminants. You can choose to peel fruits, such as oranges and mangoes. Most fruits and vegetables can be squeezed unpeeled if the skin is edible.
Celery is so easy that even the top of the leaves can go through the juicer. Celery strips can get wrapped up in the mechanism, so cut them into two- or three-inch pieces before squeezing.