Sneiks

Changed it a bit, the character is less blurry now.

It was my intention for the character to "morph" with the background, to make it seem he's a part of it. Also, his eyes pop out more that way.
You're right about the other points tho! Thank you for your critique!

I'm not an English speaker, so I just translated the Slovenian word into English and that caused the misunderstanding. I was talking about the comic clouds, the ones you put your text in. Those are clearly not made traditionally in your comic. I just suggest you to draw them yourself (digital is probably better here).
"Don't shade with black". Heard this advice a million times, but I don't really agree. Yes, black shading doesn't nook natural and stands out. But professional artists sometimes use that to their advantage. The outlines of your characters are made with black anyway, so some shading wouldn't hurt in my opinion. If you still don't wanna use black, I just suggest you make stronger shades.You can draw with a dark blue, purple or brown pencils, or you can draw with a black pencil, since the color from below will prevent the black from taking over. Do whatever you like, just make the shading more intense.
Making comics is an awesome book with a lot of really valuable information (how to design characters, composition, word-text, style, tools to use, how to become a comic maker etc.), tho it focuses more on American- European comic style. I really suggest you check it out, because you could improve a lot with its help.

I'm sure you'll improve over time. Looking good!
I suggest you draw your own "clouds". (I think you use some kind of tool here)
It doesn't take that much time but it's worth the effort since it will make the comic look way better. Draw them in some kind of drawing tool like Krita or Paint.net (those are all free) and make it transparent. I'm sure it'll look better.
Also, you could make the shading a bit more extreme here. Make the shades strong, maybe even pinch black, I suggest you use the pen you used for the lines (I suggest you make those a bit thicker too).
Also the shading on the ground can be darker too, especially behind the characters.

I suggest you read the book Making comics by Scott McCoud. I'm sure it will help a lot.