thanks for the tutorials I'll try them that will help much :D !!
The lines are unrefined and it's got a severe case of pillow shading. I'd strongly recommend checking out the Noobtorials thread on the forum: http://www.pixeljoint.com/forum/forum_posts.asp?TID=5692
Especially this, which covers several major problems you're having (cleaning the lines and shading): http://fc03.deviantart.net/fs70/f/2010/156/d/2/Pixel_Art_Tutorial_by_lucas_irineu.png
I'm trying to change it is it better like that ??