Looking for some advice on how to make appealing simple/atlas-esque map

[Broadhead]

I'm trying to make a simple overview of a large continental mass. The map's purpose is to delineate specific subcontinental zones and regions within this larger continent, but I want it to be clean, easy to read and clear. I've made this attached map as a first test and while I was able to fit names for the major zones in large type, I do think it still feels empty, and somewhat uninformative as a result. It also I thinks leaves something to be desired in it's appeal to the eye.

What are some things I can add to make the map feel fuller without necessarily adding in labels for smaller features or for political entities? And what are the design details that I'm missing currently? And finally, although this may be too broad a question: what are the actual principles of political/non-physical map design I should know as a complete amateur, in regards to both art and labeling?