Thanks for your reply to this piece and a great thanks for giving me some good advice; I'll stick to it in my next pieces. 

Well, about the shadowing methods, I tried to use different styles in both pieces to try my hand at both, moreoever to try to avoid the jagged lines. 

About the color ramp, I am still trying to improve my palettes for pixel art, I want a tutorial which teaches how to choose a good color ramp. But, thanks for all the advices.

The lineart looks good.

The shadows are lacking in consistency. It seems like you used more than one shadowing method in the pieces> I would suggest you stick to either dithering or flat color.

Also, instead of making a flat color ramp, try to use colder or warmer colors to make the lights and shades.