Political borders would make some sense (ridge line, river) and would sometimes be arbitrary (geometrical perfection or random wiggles). If your people are fractious and varied, maybe there's a mix of dozens of statelets. If all are uniform, maybe there's but one or two political units. Or if you favor the odd ravening conquerors in your domains, maybe there's a zillion subdivisions of onetime independent units, now melded into one massive empire. See my drift? Tell a bit of a story, and the geography follows plausibly.
Mechanics? Use thin lines for borders, so as not to obscure much of that nice terrain. If you have discontinuous domains - enclaves, enclaves, colonies, etc, consider color coding by rims of color on the boundaries, to cut down on the needed text. Dots do well for cities on this style, and/or simple shapes, with or without outlines. There's a great tutorial on label placement linked to in the sig of _______ (mind blank - somebody'll know).