Some plants can be multiplied merely by poking one of their leaves into some soil. To make new plants, these so-called leaf cuttings must grow both roots and shoots.
A jade leaf readily grows roots if its bottom end is put in soil that is occasionally moistened. Sometimes such cuttings just sit, making new roots but no shoots. Taking along a bit of old stem along with the leaf cutting ensures new shoots appear.
African violets and rex begonias both multiply readily from leaf cuttings. Use whole or even parts of leaves to propagate either of these plants.
Because a detached begonia or African violet leaf wilts quickly, always have your pot of soil ready before you take the cutting. And rather than using real soil, root the cuttings in some mix that is sterile, porous and moisture holding. Pure sand, perlite or a 1-to-1 mix of either of these with moist peat moss is ideal.