Thanks for your comments, guys.
I've been doing pixel art for 6 years. Honestly, I started drawing it because of SMW romhacking and because of this website. That's why I have some tricks, like using the ultimate BG ripping tool to rip my foregrounds previously done in pixel art drawing software.
At first my art was quite primitive, I didn't knew anything about color theory nor animation, but with enough practice and an internet connection anyone can unveil some secrets of pixel art. I want to write a graphics drawing tutorial for SMWCentral, but it could take a while.
Also, I don't know if I consider myself a professional, over the years I've seen really amazing works that make mines look like mere doodles, but certainly I will keep going for a while, because I enjoy doing it.
I think your artwork is not terrible, it is way better than mine a couple of years ago, you just have to try new styles, colors and techniques. Personally, I think sprites and backgrounds are the hardest graphics to draw, so having problems with them is very normal.
Since we can still post in the C3 threads, maybe tomorrow I will upload another tileset