This actually looks very good for one of your first pixel art pieces. I can see that you know the basics of shading and lighting, so that should get you far in the future. However, if I were you, I wouldn't use gradients on pixel art next time. It's generally frowned upon, because pixel art is defined as placing pixels by hand, and putting a machine-made element into your art is not the best thing to do, especially when it's as prominent in a piece as this one. By cutting out the gradient and trying to shade the screen by hand I bet you would cut the color count down to 15 or 20 colors instead of 149.
Also, welcome to PixelJoint! (and pixel art, for that matter). If you want to improve your skills, there's no better place than PJ.
very nice for 1st pixel art :)