1. Pluck a leaf from your succulent. Some of the easiest ones to propagate are graptopetalums, pachyphytums, and the fleshier echeverias and kalanchoes. Make sure you pluck the leaf right from the stem, so that none of the leaf's flesh is still attached to the stem. Fallen leaves often work, too.
2. Place the leaf in soil. I like to cover the base with just a few millimeters of soil. You're supposed to wait a few days for a callus to form. In my experience, this doesn't matter much, except with kalanchoes. But it certainly won't hurt.
3. Water the soil lightly, at the base of the leaf, every other day or so. I like to use a spray bottle and spray gently a couple times right at the base of the leaf. Yes, this is more frequently than you'd water a full-grown succulent, but you have to coddle the baby leaves or else they'll dry out. (But if you water them too frequently, not allowing them to dry between waterings, they'll rot. This balance sounds harder to achieve than it actually is.)
5. Once roots start to grow, I like to put a plantlet in its own little 2" x 2" pot. I water it based on the guidelines I explain in #3 above. Then I wait some more. Eventually (in three weeks or a month or six weeks--it varies based on the season and the type of plant), a baby plant will begin to emerge from the base of the stem, just like in the picture above. So cool!
Of course, it will be quite a while before your plantlet becomes a full-sized plant. But it's still incredibly cool to watch a gorgeous succulent go from nothing to awesomeness.
For advanced propagation techniques, I highly recommend the book pictured above, which I talk about in more detail in my Books that Succ section. So how about you, fellow succ-ers? Do you propagate from leaves very often? With great success? Any great tips you can share?