If you learn effectively from YouTube videos, I'd suggest looking beyond just map-making videos. I find speedpaint landscapes to be a good way to learn some Photoshop workflow and colour tips.

For your map, I think my biggest recommendation would be to add some texture. And by that, I don't just mean putting a parchment or stone texture overlay on the map, but doing the manual work of adding texture too. For example, you could make the water in your map get darker and 'colder' (i.e. less turquoise and more in the middle of the blue range) as it moves away from the shore. Downloading a free grunge brush set can be a really effective way of adding texture in Photoshop. I'd invite you to check out some of my work (if that isn't too shameless...) to see what I mean about the water. The same principal applies to other elements (especially natural ones, like mountain/rock, grass and trees).

And of course, shadows. Shadows make a huge difference to a map.

Hope some of that is useful advice

Wingshaw