Because we're not sculpting neutral/T poses, I find that I often have to deal with parts of the mesh being near other parts (e.g. a hand near the chest or leg). Are there any tips for quickly isolating these parts so that you can sculpt them independently? I try to use the mask brush when I can, but even then there are some tight spots where it is hard keep the mask stroke from bleeding over.
One trick you can do is go into Edit Mode, select the vertices you want to hide (or, if it's easy, the stuff you want to remain visible). Assign these to a vertex group then add a Mask modifier using that vertex group. If the mask is reversed there is an Invert toggle to the right of the vertex group selection in the Mask modifier (at least in 2.93).
The downside to the above method is that Edit Mode can really groan with high-poly meshes.
There is probably a way to use Face Sets for masking as well but I haven't experimented yet. Definitely something to look into though!
...it is hard keep the mask stroke from bleeding over.
You can, in the case of an arm for instance, mask only the hand (or whatever part you can easily mask) and then go to Mask > Grow Mask (I'd recommend Assigning a shortcut key to it, because SHIFT+R to repeat the last operation doesn't work in Sculpt Mode!).
This works in 2.83 +, but I don't know exactly when this was first introduced.
Excellent suggestions from spikeyxxx and coyohti! You can also use the "grow by topology" tool in sculpt mode. Take a look at this video for a demo: https://cgcookie.com/lesson/posing-2-8
These are all great suggestions! I like the face sets suggestion (with face set automasking) because it makes it easy to jump around, but it seems that it doesn't work with dynamic topology (yet?). I get the sense that there's a push towards remesh-based workflows anyway, so I might start experimenting with those. Expand Mask by Normal is almost exactly what I had in mind, because it seems to expand along the edges/faces rather than distance, but for some reason it stops when I reach a bend in the mesh and creates a few mask artifacts that I have to clean up. Maybe those are bugs that will be fixed in future releases? Grow Mask seem to be the most versatile solution for now, but takes quite a few iterations to get the desired result. I'll probably end up mixing all these approaches based on the circumstances. Thank you, coyohti, spikeyxxx, and theluthier!