
i figured somebody else might appreciate this advice, so i hope it’s okay if i post this publicly!! i’m really sorry if it isn’t, just let me know jglsdg
first of all, thank you so much! (and school went fine, thank you!) i’m really glad you liked it – that means a lot to me, especially from someone whose art i admire! but if i’m being honest with you, backgrounds is my weakest point too!! sometimes i just get lucky, and that was one of those times.
but, i can tell you what tricks tend to work for me when it comes to making functionable backgrounds! i find that for dynamic pictures that cover a lot of area in the background, having a slight curve works to give it more perspective, and it draws attention to the middle of your drawing if that’s where you want the focus to be.
another thing that’s very very important is knowing where your light source is, and what colours it’s giving off! if you look at that last drawing, you can see how the source of light stays consistent with where each of the boys are standing:

i’m obviously nowhere near perfect with light and shadow placement but i hope you can sort of see what i mean! knowing where light is going to fall on the people in the drawing makes the difference between people looking like they’re just standing in front of a backdrop, and people looking like they’re actually immersed in the scene. finally, one last piece of advice i can give is that I try to match my backgrounds to how detailed my characters are with colour/shading/etc. there’s nothing too special with them in this drawing, so i made the background kind of blotchy and simplified to keep the attention on them and not make it look out of place, if you see what i mean?
as for the actual colouring of the background, most of the time layers tend to work best for me!! i start with a base colour (dark purpley-blue in this case) and build on top of it starting with what’s closest. the poles came first, then i made the mountains/islands, then the water-horizon line and then the clouds! it’s also a good idea to start with a base colour for each of those things, then add dark and light bits once you’ve figured out your light source.
sorry if this is hard to understand fjlksdg i hope i helped you a little bit, at least!