I hope this is the right forum…
I find this one to be very tedious, mostly because 2 flat pieces of geometry overlap. So when I attempt to play with their weights they get all entangled 
Any advice on how to approach it?
On the 2nd image above, one can see the geometry from below, coming through the top geometry
I have tried to paint above and under until both are red, not easy. And the results are quite messy.
Thanks guys,
JDL
Use a Mask modifier to hide faces while weight painting.
But you need to create a vertex group to assign it to the Mask modifier:
Press ‘Invert’ to invert the visibility.
You can also use a Mask modifier to hide parts from rendering. E.g. the skin under clothes are masked. This way you don’t have to worry about overlapping geometry.
I never knew about this modifier. I guess I never came across an opportunity to use it.
Thank you so much for the advise and for taking the time to explain 
Cheers!
JDL
There is a face selection mask tool in weight paint mode (button is in the header). It makes the mesh visible and you can only paint vertices of selected faces. It also enables the Show/Hide feature which is done in edit mode (H, alt-H, shift-H … also found in the edit mode mesh menu).
With face selection mask enabled you can then tab between weight paint mode and edit mode, hiding geometry and only painting vertices of selected faces.
There is also a border clipping tool available in both modes (alt-B toggle) hides everything except what you box select. Not as precise but useful (quick).
Thanks a bunch for the additional advice, Larry
Btw, I know H, and Alt H, but what’s Shift H?
Now, about the status of my project… unfortunately even after making sure that I had painted both sides totally, the geometry below continues showing through. Not as much, but about 50% 
I am considering using Shapes to “manually” tweak the geometry, ensuring they won’t go through each other.
Any other ideas?
JDL
Actually… I am now simply “adding” weights in Weight Paint mode, on the neighboring bone, and this is fixing that problem (rolling eyes - why didn’t I think of it before?)
JDL
Rolling eyes -LOL- I’ve almost given myself brain damage from slapping my forehead so much since I got into this stuff.
Shift-H hides what is not selected.
Btw most (not all) shortcuts can also be found in a menu somewhere, and most menu items show the shortcut when you hover on it.
Mmmm I guess I spoke too soon
That idea about painting the neighboring bone only went so far. I have discovered using the “Vgroup” button. Which allowed me to only paint one vertex group at a time. I really thought this would do it for sure! But it did not
Look how the under geometry goes through the one above
Now looking from under…
Btw, just so we’re on the same channel, I did try isolating faces and groups of vertices with the techniques suggested earlier, but it didn’t help me either It was great to learn about though
Here’s the last tip I have to offer.
The next step is to manually check and clean your vertex groups. When a vertex is “painted” with a weight value it gets assigned to that bone’s vertex group. If you paint it back down to zero it still remains in that group. This is known to cause issues. If you accidently painted vertices then painted them back to zero you have to remove them from the group as well.
In 2.49 you had to remove stray vertices manually in edit mode. In 2.5x there is a “clean” button in the tool shelf. It works pretty well if you mind the limit control in the panel that appears when you activate it. Default setting is .010 but that’s too low. Vertices that don’t show color can still have enough weight to not be removed at that setting (for me anyway) so crank it up.
The best sure-fire method is to go into edit mode and use the Vertex Groups controls (in object properties). There you use the select assign remove tools to check every group and get your vertices sorted out for sure no doubt once and for all.
There used to be a (no menu) shortcut for a quick way to see what vertices are in which groups but I don’t remember it and don’t know if it even exists in 2.5x. Maybe someone else knows. (I’m outta time or I’d find out now).
Anyway, this is the last step before deleting all the groups and starting over. I have been taking it for granted you’re sure about your bones and stuff so nothing else besides weights/groups is the problem.
I hope this helps you out. I should have mentioned this stuff last post. (Ha, mentioned he says :)). If this doesn’t help you’ll have to make the file available so someone can take a look.
-LP
Hey, I find this thread really helpful because I’m also finding the weight painting process pretty painful. About vertex groups: Can I then (after manually setting them) mirror my joint weights? Will it mirror the vertex groups as well? Just wondering.
Thank you so much for your help Larry
I’ll check very carefully those vgroups.
I may have to wait a couple days before I can take care of this
JDL
Hey Larry, I did clean up those weights by creating new vgroups (I kept the same names though), and things are looking much more promising now
Thanks again
JDL
Actually… just cleaning up the weights wasn’t good enough
So far what worked the best was to add more bones, therefore more work But at least more control too 
JDL