I used to put forms on those little wooden dowel rods and only make thin nails. They pop off easy and are reusable. Then you can take a florist pin (the kind with the wooden stake and a wire) and glue the tip you made to the wire. Poke it in some florist foam and put it in a decorative pot. That is what my avatar is--my handpainted art display.
The very best way bar none, in my opinion, for practicing sculpting is on a real live person.
Lets face it, sculpting is what you do every day on top of a tip except that there is no tip.
I trained all my salon techs to sculpt the following way ... it is easy, quick, practical and non stressful. EVERY time you have a client with one broken nail .. SCULPT IT to fix it. That way you get the chance to do one perfect sculpt at a time (instead of 10) and the time to do it right. Do this for a few weeks and you will be sculpting away like a pro.