With a pen and ink type map like this you want to try to give it a cohesive quality. You want it to all look like it was drawn by the same person with the same inks, and the same pens, at the same time, and getting it wrong shows up much more than with a lot of other styles.

Try to avoid scaling symbols as a drawn symbol has a very particular visual size to it. If you see two scaled versions of a drawing next to each other, they will look wrong. If you need a big tree and a little tree, they should be drawn at those sizes so the big one has more detail. Similarly, if you take two symbols drawn at very different sizes, and scale them to be closer, they will likewise probably look off in this style. Consider absolutely everything: the trees, coastlines, rivers, cities, labels, borders, and even the decorative dragons if you have them. Consider levels of detail, size, line width, contrast, etc.

Variations in blur, resampling, or anti-aliasing, are also very noticeable. Again this tends to result from combining symbols from different sources and sizes. That's not to say you can't mix symbols from different sources, you just need to be careful about picking ones that match.

Blur or excessive antialiasing in general is bad. You want everything to be nice and sharp, within the limit that you also want everything to be equally sharp. Good strong contrast is also desirable.

I try to do maps like this in pure black and white to start, and then add colour once I am entirely happy with the black and white. I generally work in vector graphics, but If I were doing raster, I would probably go for a very high resolution while I work in black and white, and then switch to greyscale or colour and downsample it.

Your terrains seem to form solid looking "lumps" often with boundaries that run along rivers. It gives your map a bit of a "patchwork" look. If you don't want to go into climate modelling, try to just give things a more "amoeba" look and don't follow rivers so much. If anything I'd be more inclined to run rivers through the centres of ecosystems than along the edges though being to consistent in doing either would look odd.

A fairly rudimentary climate model would be to pick areas as being "wet" or "dry" Wet areas tend to be forest, dry areas tend to be grassland/shrubland or desert. Areas around humans tend to get turned into farmland or pasture. Wet areas have rivers forming. From there they flow downhill and merge with other rivers as they go, until they reach the sea, they can pass through dry areas just fine if that's the downhill route, they just won't have many tributaries there. For a bit more depth, pick a prevailing wind direction, make the windward side of mountains wet, and the leeward side dry. For large landmasses, the interior will also tend to be drier. There's a LOT more that can go into a climate model, but that one will give you some ideas as to where to but things so that they look kind of natural and consistent.