Here's a reference i think is good:
ClickNevermind the background. ^^
The lines are now colored instead of just black.
And I'm using 2 shading colors and a slightly lighting.
@Malte
Your 1st suggestion: So you mean the head and neck connects as one line?
Something like the first one in this but should look like the second one:

I just recognized that. Thanks Malte. :^.^:
And the 2nd: There's a reason why the iris are thinner. The characters would look to another direction instead where they should look. But it can be also the oval thing that make them do so. Just remembered their eyes should be a circle too. I just keep forgetting it.

:
Though, I just read your suggestions today but finished another pic yesterday, so I couldn't go with your suggestions.