1. Okay, now the very first thing I do when making every icon is look at the original picture and ask myself what I like most and least about it. In this picture, what I like the least are the wrinkles around his mouth the expression is making, so I using the healing and history brushes I make them less prominent. When I intend for the face to be the subject, it's not entirely unlikely for me to retouch them a little. Not a lot, just enough to smooth them out a little bit. And what I like most about this is the column behind him, I think it makes a really cool framing effect. It's definitely going to factor into the way I crop him.
2. open 300x300 canvas. I work with a large canvas primarily because the colouring effects I use tend to make things look grainy and if you make it large to begin with and then resize it to 100x100px you'll never have to worry about that again.
3. crop. These next few steps are going to look ridiculous, but it's important that you do them all.
4. duplicate and set to 'soft light'.
5. make a selective colour layer. To lessen the intensity of the reds we're going to +5% cyan, -15% magenta and -15% yellows. I sometimes play around with the neutrals a little bit, but I'm not going to this time.
6. make a curves layer, do nothing and set it to soft light.
7. now between the original and the duplicated original make a hue/saturation layer and pump the saturation right up. This depends on on how saturated I want the final image to be and how saturated the original was, but usually something between 40% and 55% does the job. I'm going for 45%.
7. now underneath the hue/saturation layer make a curves layer. You'll notice that the picture is probably very very red at the moment, we're going to try and counteract that with some cyans, so in the greens I put the lightest point to output:255 input:207 and for blues I made the lightest point output:255 input:164. "Huh? But the reds aren't gone yet!" you say angrily. Perhaps, but I then went back to the selective colour layer and changed the red settings to +44, -15 -10 and -20, so that should have it mostly fixed for now.
8. between the hue/saturation and the curves layer we're going to make a solid colour (#f9f6ed) layer. Invert the mask and using a large soft brush (with flow set to something low like 3% or 5%) we're going to lighten him up. Here I'm trying to generally stick with the original lighting of the picture, which is from either side, but I'm not leaving his shadows totally untouched.
9. now, above the creamey layer we're going to add in a pure white layer. I've only added this step in very very recently. As in, after reading neversleeps's light splodge tutorial at icon_crack recently. Invert the mask, make a few brushes here and there using a hard 70px round brush (having one go through up their forehead is usually a good look :D) and then blur the mask with a 23px radius. Then mask away all of the bits that look weird and add in little bits where you feel it's necessary.
10. on top of all of these layers make a brightness/contrast layer. Always +5 brightness (minimum) and then adjust the contrast to whatever you think looks good. I ended up with +50%
11. And now it's time for fine tuning. After adding the contrast I felt that the yellows were getting a bit too intense so I used the curves layer (between the selective colour and the brightness/contrast) and added in a little bit of blue. I also thought the green bushes on the edges weren't bright enough so added another curves layer on top of everything, masked it so that it just affected the bushes (and some of his shirt) and then lightened them. :D
12. merge this all onto a new layer, save .psd, shrink to 100x100px, save as .png, undo resize and then resave as .psd just to make sure that you've got the full version
some other icons made with this technique
To be honest I'm not totally in love with the result, but these are the general steps I go through when making every icon.