I'll offer a quick critique. I am not a fantastic oil painter, but I have done enough to offer some advice. First....it looks as if you have used a straight black for the background. I would suggest mixing your own darks and laying them in. Its more interesting visually that way.

2nd...a mistake a lot of people make is blending the hell out of things...just for practice sake try mixing your proper color/value...put it on with the desired paint stroke...and LEAVE it. No blending. Eventually layering will "build" the image you want gradually. When you apply the paint, go for a SILENT brush technique..meaning that your bristles either barely touch, or don't touch the canvas at all.

3rd...while beginning, use a LIMITED palette with a maximum of 3 colors plus white. You would be amazed what you can do with them. If you would like a list I have had good success with, I will be happy to post them.

Hope this helps