From this to this
Now I cropped, resized and sharpened it once since the original was already sorta sharpened.
to
Now that we have our base we can start playing around with it. We duplicate the base and set it to Soft Light Opacity 100%

I think she looks a bit too pale so I add a peachy gradient to give her skin some glow and set it so Burn Opacity 100%

Next I add another gradient and set that to Burn Opacity 100%

I like to add a lot of color gradients to the icon to make the colors pop out. So next I add another one and set it Burn Opacity 22%

I also try to incorporate colors that are already in the icon and since Emilie is holding a purple flower I use this purple gradient and since the color is really heavy I set to Burn and lower the Opacity to 8%

But I don't want the icon too dark so I brighten her up by using a light pink gradient and setting it to Soft Light Opacity 100%

Next I add this gradient and set it to Exclusion Opacity 100%

Now I didn't want the icon to be too white so I add another gradient and again set it to Exclusion but change the Opacity to 10%

I add this gradient again set to Soft Light at 10%

Now the icon is complete and you can finish here if you want, or add some text and you're done. But I wanted my icon textless and I decided to bring out Emilie's eyes a bit more. So I added a New Raster Layer (Layers>New Raster Layer) and with my Airbrush tool I colored in her eye with the color #40FFFF. I know it looks a bit weird, but set the layer to Color and you can change the Opacity to your liking. Since I wanted her eyes to pop out but be very subtle I left the Opacity at 12%.

and Voìla your icon is done, now sometimes your icon can come out a bit too blury like this one below

You can do three things to fix that.

A)Adjust>Sharpness>Sharpen

B)Duplicate your icon and Adjust>Sharpness>Sharpen (or Sharpen More) and then play around with the Opacity depending on how you want the icon to come out. I used Sharpen More and changed the Opacity to 38% at Normal.

Or the last and most comsuming method C)Duplicate your icon Adjust>Sharpness>Sharpen (or Sharpen More) and then use the Soften Brush to soften the areas you want. I used it on her face and on her hand.

Orignally I stoped after I brighten her eye, but since the question for crispness was asked I added the last bit. Hope you enjoyed the tutorial. =D

Icons using the same/similar technique