Check this. Also post in the WIP forum to get help improving pieces. Read other peoples' WIP threads, also here.
Your high color counts can be explained by the use of soft tools (brushes) as in Space, or might be accidental as here. Possible culprits: opacity not 100%, auto anti-aliasing not disabled on some tool (pencil, eraser, bucket, selection), saving as jpeg, resizing.
Also as a beginner, you should work on much smaller pieces, like 100x100 and below. Pixel art is about controlling each single pixel in a piece. 100x100 = 10,000 of them: that's a huge lot already!
I really don't know how to draw as you or any else artist. Can you give me some lessons or something that can help me to understand. (sorry if my english bad)
All your pieces have 100s of colors. You're doing something wrong.
Thank you, i hope it will help me :D