There is no "one" way to sculpt as you can see from all the replies
here by different artists.
For me the most important point when sculpting hands is to get the size
right. In my earlier days of Alpine, I used to catch flaks from modelers
saying that the hands I sculpt are too big. So first thing is to get the size
right. Forget the anatomy chart and all that measurements. It has to
"look" right. The detail comes after once you have the right size.
As other artists pointed out, carving is a good way to approach hand
sculpting once you have the basic shape ready.
In order to really get the hands looking like hands, I recommend you to
sketch out the hands exactly how you want from looking at real hands.
While you are drawing the hands, you begin to understand the shape,
proportion, and how you want to sculpt them.
If you are making hands from the image you have in your head without
looking at the real hands, you get exactly what you ask for: imaginary hands
and not realistic ones.
Hope it helped a bit.