When I am sculpting hand or heads, I have the tougest time. These areas are not very much fun at all... until you start to get the hang of things. There is a light at the end of the tunnel, and once you are there, you will be enjoying sculpting once again.
The best way to get started... is clip of the hands and heads from other kits, and apply them to your own minis. This obviously does not teach you to sculpt them, but it does teach proportion, angling and posing. It also allows you to focus on other areas of the model, without becoming discouraged.
After a while, while borrowing hands and heads, you can start sculpting them. If you have learned a bit from sculpting the other stuff, then you can apply what you have learned to your sculptures. When sculpting large hands, I sometimes sculpted right overtop of other model kit hands, to get the right proportion. After a while, you wont need to do this, but the lesson here is do not be afraid of borrowing. There is a lot you can learn from it.
The advice of sculpting with a non-hardening material is excellent as well. To this day, I use a mix of sculpey and green stuff, so my heads and hands have a much greater drying time, giving me more working time, in case I am not fully satisfied. If you use Sculpey or Super Sculpey for the hands and head, try boiling these bits instead of baking them. Its a little more controlled, and bakes the parts just the same. You may notice doing this makes the pieces potentially more \"crumbly\", but you should not notice this with smaller areas.
Hope that helps, and good luck to you.
Sophie.