1. Duplicate your base, set it to SCREEN 90%.
2. Curves! Go to Layer >> New Adjustment Layer >> Curves. I've made screencaps of how your lines should look, because I always get really confused when people just post a bunch of numbers.
3. Go to Image >> New >> Layer, fill it with #959595 and set it to COLOR BURN 71%.
4. Now the icon looks really greenish/yellowish and ugly. This is where the beauty of selective coloring comes in. A lot of people rag on selective coloring, but used correctly, it's one of the most useful tools in Photoshop. I LOVE IT. Anyway, we're going to make Dean's skin look more flesh-colored. Layer >> New Adjustment Layer >> Selective Coloring. Input these values at 100%.
5. Layer >> New Adjustment Layer >> Brightness/Contrast. Up the contrast to 23.
6. Add any textures you want. I used one of these grid textures; if you made this let me know and I'll credit you. It's a very subtle effect on his particular icon. I erased the grid marks from Dean's face and just left it in the bottom left corner.
To sharpen I usually go all the way to the bottom of my layer pallete, duplicate my base, go to Filter >> Sharpen >> Sharpen, and set that to around 40%, or whatever looks sharp enough. I always sharpen at the end, because you keep duplicating sharpened layers, your icon will come out looking more and more jagged.
If you have any questions or are interested in the .psd, see this post at misty_creates.