This is especially important when juicing root vegetables, or vegetables that grow close to the ground because of impurities in the soil. Also remove any peel that is bitter such as watermelon peel. Look for vegetables and fruits that appear to be juicier. They often will feel heavier because most of the weight in fruits and vegetables is water. Some foods do not have much liquid and therefore do not juice well.
Examples are bananas and avocados.
The centrifugal juicer. This is the most common type for home use. It grates the food in a basket, then extracts juice. The trituration-style juicer. This one creates a pulp from the food, then extracts juice from the pulp.