Today i found it really helpful using polygroups as a way of isolating the thing we are currently trying to shape during 3D modeling. Polygroups and masking are an excellent way to save in a sense layers (like in photoshop) during modeling so we don't mess up work we already created.
Here's a proportion example i sketched today in 3D in about 1hr total. I spent first 30 minutes blocking in shapes and the next 30 minutes trying to block in basic silhouette.
I found it helpful during blocking to choose an area with a size close to what i wanted like say the head, then for other areas used that as a reference for the other sizes while looking at reference. Example this other area is one and half heads etc. Also, I found it helpful after first 30minutes taking a brief break and hand drawing a rough silhouette ontop of a 3/4 view picture of mesh. In ZBrush the clip curve brush was helpful in helping make silhouettes.
(rough blocking (right) , silhouette sketch (mid), rough silhouette (left) )
(To make a polygroup on a masked selection. First mask the selection then go to the polygroups menu and click group masked. During modeling to only show a polygroup press ctrl+shift and click on the mesh part, it should now only show this polygroup. )
A helpful technique that i used was to show the polygroup then mask the entire selection then ctrl+shift click away from mesh which should bring back all of mesh. Then ctrl+click away from mesh to invert selection. Now we will be able to just work on the unmasked portion.
Note when using insert brush it comes with its own polygroup. But if we duplicated the inserted mesh using the transform tool (ctrl+shift+click on mid circle to duplicate) we may want to put this new mesh into its own polygroup.
Here are some images i made of an example of creating a polygroup and mask.
Hope you find this helpful
José Manuel Fernández Oli (nibbledpencil dot com) (Who i first learned about researching 3D scan online images as a great reference for modeling)
Michael Pavlovich (i learned about polygroups and duplicate via transform tool tip from watching his online tutorial videos)