Try practicing with other icons using the same art program that you used to make this. Also, try and experiment with the different methods or options (such as shading, filters etc.) the program has to offer and you'll eventually get the hang of it. (and master it, in the long run) That's how I eventually made my first skin.
Besides, you should be glad you did it in freehand, i mean, a lot of people just do cnp and\or recolor and sumbit to this site without effort.

