=Spoiler написал(а):

STEP ZERO: CHOOSE A PICTURE
from this picture (which I got from semantic_spaces at this awesome gallery)
Choose a picture! I picked a nice, bright, outdoors cap. I recommend that you crop towards the end rather than at the start (you get a better picture quality if you crop later!), but for the purpose of this tutorial I cropped right at the start.
STEP ONE: SMUDGE
Here I used the smudge tool to clean up the background a bit. I smudged over the person sitting on the edge of the icon, since I wanted focus to be on the characters in the middle of the icons. You can use a combination of the smudge tool, the clone tool and textures to get really nice backgrounds, but for this tutorial I just did a quick smudge.
STEP TWO: SCREEN
Copy the base image twice and put both copies on screen. The first copy I put on 100% opacity, the second on half of that. This will be different from picture to picture. The purpose of this step is to make the image brighter.
STEP THREE: SOFT LIGHT
Copy the base image again, make sure this new copy is on the top of all the other layers, and put it on "soft light". Soft light adds back some of the contrast and shadows that got lost when we brightened the image in the previous step.
STEP FOUR: LEVELS (ON COLOR)
(see which settings I used here)
Next I used levels to adjust the coloring on the icon. I put this levels layer on "color", which gives a nice result. It's important not to change the RGB values when you have a levels layer on color mode, or you'll get some really strange results.
I left the reds unchanged. The green I decreased in the shadows (which gives the shadows a purple coloring) and slightly increased the green in the highlights. The blues I decreased a bit in the shadows (making the shadows more yellow) and increased in the highlights.
Working with levels to color icons is easy to learn and extremely easy to use once you've mastered it. It helps to have a basic understanding of the color wheel first.
STEP FIVE: COLOR BURN
I copied my base layer again, dragged it to the top, and put it on the blend mode "color burn" at a low opacity (I chose 8%). This adds color and depth to the shadows.
STEP SIX: PAINT IN PURPLE
I created a new empty layer (Layers -> New -> Layer...), picked a purple color and painted a purple stripe along the top of the icon. I used gaussian blur to blur this layer. You can see what it looked like above (I added a gray background here just to make it easier for you to see what the layer looked like). Put this purple layer on soft light 100%.
As you can see, this made the painted part look more purple:y.
STEP SEVEN: PAINT IN PURPLE
Copy the purple layer once, put the copy on blend mode screen 25% (pick the opacity that looks best for you). This brightens up the purple part, as well as add more purple to it!
STEP EIGHT: PAINT IN WHITE
Here I created another empty layer, painted a white stripe along the top, and then I gaussian blurred it. Here I added the black background to the first picture just so you can see what it looked like better. Put this white layer on soft light (I chose 100% opacity). This brightens the top of the icon, which gives the icon a lighter feel.
STEP NINE: PAINT IN WHITE
Copy the white layer twice, put both copies on soft light 100% opacity. Now there's three white soft light layers in a row in total. This brightens the top of the icon considerably.
STEP TEN: PAINT IN WHITE
Copy the white layer again, put this copy on overlay at 100% opacity. This both brightens and accentuates colors.
STEP ELEVEN: DESATURATE
Copy the white layer again. Put it on blend mode "saturation", since white color = no saturation, this will desaturate the top of the icon. Since I blurred the image, the color is spread out over the top and no part is completely covered in it, so no part of the top is completely desaturated.
By desaturating the top of the icon, I bring back the focus to guys, who are more saturated and therefore more eye-catching.
STEP TWELVE: PAINT IN WHITE
I wanted the edges of the icon to be brighter as well, to really bring focus to the middle of it. I created a new empty layer, painted with white color along the edges, gaussian blurred it, and put the layer on overlay (I chose 100% opacity).
STEP THIRTEEN: DESATURATE
The previous step left the edges a bit too saturated, so I copied this new white layer and put the copy on "saturation" for the same reason as I explained in the 11th step of this tutorial.
STEP FOURTEEN: FILL LAYER (COLOR BURN)
I added a fill layer (Layers -> New fill layers --> Solid) with the color you see above (#FFF5E6). I put it on blend mode color burn, which adds shadows and enhances the fill color in the picture.
STEP FIFTEEN: FILL LAYER (SOFT LIGHT)
I created another fill layer (#31FFBE) on blend mode soft light at a low opacity (10% in this case). This added the fill color to the icon and it also brightened the icon up a bit.
STEP SIXTEEN: MULTIPLY
Merge all layers. Copy your new layer, put this copied layer on blend mode multiply and lower the opacity as needed. I chose 20 percent opacity. Multiply darkens the image, so it's not as overly bright any more.
STEP SEVENTEEN: SHARPEN
You're actually not supposed to sharpen until the very end (so that you lose less picture quality than you would if you sharpened at the beginning (sharpening is a destructive process)). For some reason I just thought I was finished here and so sharpened a bit early. Luckily it didn't really matter in this case.
Merge all layers. Copy your image, use the high pass filter on your copy (Filter -> Other -> Highpass) at 0.3-0.5 radius. Erase the background and other things you don't want any sharper. Put the high pass layer on soft light or overlay. I chose 0.3 radius at soft light 100 percent, but you might end up using different settings for your picture.
STEP EIGHTEEN: PAINT IN A NEW COLOR
I decided that the green jacket weren't green enough anymore, after all those coloring steps, so I created a new empty layer, picked a nice dark green color, and painted over the jacket. I put this layer on "color" at 75%. This changed the color of the jacket to something I liked better.
STEP NINETEEN: PAINT IN GREEN
I created a new empty layer, painted a bright green in the corner, blurred it, and put it on screen (100% opacity). There were already a lot of green in the icon, and I like green, so I decided to add some to the corner that was sadly lacking in green.
STEP TWENTY: PAINT IN A MUTED GREEN
As a last step, I used the eye-dropper tool to pick a nice color from the wall in the background. I then created a new empty layer, painted with my new color along the top, blurred it, and put it on soft light (100%). This both brightened and colored the part I had painted.
And we're finished!
Previously posted here. See the rest of my tutorials here