You are getting better and better... Keep practicing. Look at other icons, compare, learn more about shading, think from where should the light come, and keep strengthening the lights and shadows and don't forget to smudge from time to time (but do not exaggerate). Btw, what program do you use? I hope Adobe Photoshop!
Maybe I should concentrate on making my own Icons instead of recoloring Icons that already exist. It feels a lot better. 
