How to mark the seams of UV maps to edit textures in external programs? I am working on texturing a complex object, but do not like the blender's painting tools. So, I tried editing it in an external editor, but don't know how to know in the external program where the seams are. Is there any workflow for labeling different pieces of the unwrapped faces so that in the external program you can focus on painting each of those pieces? All advice is appreciated!
If you are painting some textures that are a little bit more complex, you might want to consider doing that on the 3d model in 3d. There are plenty of tools for that in a lot of 3d packages these days, Blender included. Obviously if the textures you need are simple, using an external image editor is a very valid option as well. Especially for every day simple objects. 

The usual workflow is to export the UV map as an image and make the textures using that as a guide. 

You would simply enter edit mode, select all to view the UV map, go to the UV Editor and choose UVs menu on the header, then Export UV Layout:



You can chose desired options and save the file then.

It is then usual to open it in an external editor and have it as a top layer while working on the texture so you can see the location of the UV islands while you work and disable it once you save your texture: