Hello, welcome to pixelation!
I think nobody has answered you yet because your pieces are already quite good with no huge apparent flaws. So congrats on that, your art is already readable, nice to look at with good use of colors!
If I may, the small character with the long hair feels a bit confused, try maybe to simplify the hair texture to get a more "united" feel, less pure texture, more volumes.
On your last green landscape, the clouds that constitute the background lack a sense of direction. You could draw the curve which they're supposed to follow and then on another layer shape the actual clouds and give them a cleaner finish.
On your Pokémon-like creature, the shadows feel muddy. Picking a color that's a bit darker and more saturated will improve your piece overall. You could also play with hue shifting to make it more interesting (this PJ thread is very enlightening
http://pixeljoint.com/forum/forum_posts.asp?TID=10695Also a good way to improve would be to participate to some challenges; pixeljoint.com holds a different pixel art challenge each week
