You can simply take a leaf that has fallen from your succulents or gently remove one off the stem. Make sure to use a twisting motion to pull the leaf off the plant entirely and avoid breaking it. Poor cuttings can result in the leaves not being able to sprout roots.
Put the leaves on a paper towel until the cut ends dry out so that they will not rot when planted. After a couple of days letting the leaves dry on the paper towel, transfer them to lay on top of some succulent or cactus potting soil.
Give the leaves bright and filtered sunlight as well as mist them with water whenever the soil dries out, probably a couple times a week. Roots will start sprouting and baby plants will appear after a few weeks!