Plokman's Backgrounds and Sprite testground

[Garamonde]

I also notice you use the line tool a lot in most everything. Don't do that as it makes everything look blocky and unprofessional. You want things to have more curves so they'll look natural. One solution is to roughly sketch the basic shapes of your sprites by hand, add details and then refine the outlines. This way you shouldn't end up with anything too stiff, hopefully.
There also isn't much in the way of shading, and what little there is doesn't show any depth. Most of it's very flat. You don't shade an object just to shade, you use shading to help define the shape of the object.
You also need to learn about lightsources (which is explained in the spriters dictionary), because your gems, as well as many other parts of your backgrounds are pillowshaded and have banding. All in all it's really just a bunch of straight lines with flat shading. Black outlines also help in making it look flat, so try to get rid of the black, and instead make the lines a darker version of the base color (make it darker than the shading too).
So with that ends my observations. Hope that helps at all!