I'll preface this advice with an observation: most cartography advice out there is actually geography advice. That is, it is advice on creating a believable world, rather than how to map that world. So something like "rivers should join together as they go, not split apart" is geography advice. It's telling you something about how rivers work, not about how to properly map whatever rivers there are in your world. My advice below is meant to supplement this advice on geographical worldbuilding with some thoughts on the question of how to make maps of your world.
Even something as seemingly basic as geometric accuracy (e.g. consistent lat/long coordinates) may not be a priority. Those medieval "T&O" maps weren't drawn like that because the mapmakers were ignorant of the real shape of their world (sailors were using impressively detailed charts at the same time) -- they look like that because the goal of the map is to show the world as an orderly creation centered on the holy land, thus expressing the medieval Christian worldview.
I would recommend that you ask yourself:
1. Who is making this map? Are they a trained cartographer, or a newbie? Are they a leader or rebel with an axe to grind? Are they someone who has absorbed all the conventional wisdom of their culture? Get inside the perspective of the cartographer and think about how they would see the world, and what their agendas and skills are.
2. What tools do they have at their disposal? Is the map made with pen and paper? rock carving? a printing press? a computer? This will shape the style of the map drawing -- certain shapes are easier to make with a pen than a chisel, for example.
3. What knowledge (correct or not) do they have about the world? What things can they find out easily versus where are their gaps? How did they get that information? This is especially important in fantasy settings. Take a look at medieval European and Chinese maps, and in particular how they represented each other's subcontinents.
5. In what context will this map be found? Will it be printed in an atlas? hung on a wall? folded up in someone's desk? part of a longer reference text? a propaganda poster? Any mapmaker will be thinking about their intended audience and how to communicate best with them.
Use the answers to those questions to clarify your answers to the specific choices that need to be made in assembling a map:
- How much area will this map cover, at what scale?
- What projection will your map use, if it's broader than a city or small region?
- What features will be made prominent on this map, which will be backgrounded, and which will be left off altogether?
- What kind of symbols will you use to represent those features?
- If there are areas of uncertainty or lack of knowledge, how -- if at all -- will they be indicated?