My Devil's Pie 2 configuration in the hopes that it might one day help someone.

rules.lua

-- debug_print command only prints anything to stdout
-- if devilspie2 is run using the --debug option!
x,y,w,h = get_window_geometry()
xs,ys = get_screen_geometry()
debug_print("There are "..get_workspace_count().." workspaces with a total area of "..xs.."x"..ys..".")
debug_print("Window '"..get_window_name().."' ("..w.."x"..h..", belonging to '"..get_application_name().."') open(ed) at "..x.."x"..y..".")

-- Make sure windows open on the external monitor.
if (get_screen_geometry() > 1600 and x < (1600-w+50)) then
  debug_print("Moving to viewport 2 because window's x=" .. x .. " < monitor border at 1600-w+50="..(w+50)..".")
  set_on_top()
  set_window_position(1600+50, 50)
  -- set_viewport(2)
end

-- Make Evince always appear with the same size.
if (get_application_name()=="Dokumentenbetrachter") then
  debug_print("Changing Evince's size to sane values.")
  set_window_geometry(x,y,1200,850)
end

-- Make Firefox always start maximized.
if (get_application_name()=="Firefox") then
  debug_print("Maximising Firefox.")
  maximize()
end

debug_print("------------")