Well, the easiest thing to do, if you know you want to sculpt a figure with clenched fists, is to simply model him that way in the first place. Model the base hands as solid masses, and “sculpt” them into fists.
The second easiest thing to do is to model separate fingers, but model them into a “clenched” position from the start. This will make it easier to sculpt them into a fist from the start.
Next, you can take the approach of modeling the fingers in an extended, relaxed position (which has the benefit of making the figure’s hands poseable for more than one position, if you anticipate the need). Then, hide everything but the hand, and use masking and the transpose controls to “bend” the fingers into place joint by joint.
This will take a bit of effort, and the end result for such a fine detail area will be far from perfect. This really only gets the appendages into a “ballpark” position, and you will have to further sculpt the area to make it look right.
Hints: Start at the lowest subD level, and use the move brush with little or no falloff, to pull the individual finger verts into a more accurate position (it is helpful for this purpose, to have a base finger mesh divided into 3 logical sections, with 2 clean intersecting edge loops…the more geometry you put there at the base level, the more complicated it will be to pull these points into position). Then, run over the fingers lightly with the inflate brush with low falloff to make sure the digits have the proper mass. Once the form is correct, start moving up SuBD levels for detail sculpting.
Finally, for the absolute best results, you could rather painstakingly create a detailed Zsphere hand armature, with accurate articulated joints, positioned appropriately under the mesh( or create your mesh as an adaptive skin from that rig in the first place). Then, bind the mesh to the armature skeleton in the rigging pallet, and manipulate the zsphere skeleton to pose the fingers.
This will result in probably the easiest and most accurate “posing” of the digits, but you will still have “cleanup” work to do. No matter what you do, a “posing” process will cause you to lose much sculpted detail in the fingers, so it would be better not to do any detail work on them until they are posed in the proper position, and the form is correct.
[sorry for the book here]