Start by cropping your image, but don't resize yet. If you want, sharpen it a little with Filter → Sharpen → Smart Sharpen. Only a little, though! So this is what we're starting with:
Now the tedious part begins. Go to View → Fit On Screen. Select the Polygonal Lasso Tool.
Find the outline of the shape you want to start cutting out. Click at the very beginning of it and start moving the Polygonal Lasso Tool along, clicking wherever you need to change your angle. Then delete everything that isn't part of the shape you're cutting out. Here's the start:
Here's what it looks like while you're outlining:
Finally, you're done!
Resize it now. In this case, we're going to resize to 80 x 80 pixels, then Canvas Size to 100 x 100 pixels. Slap a white background behind it for now for ease on your eyes by creating a new layer underneath it, then filling that with white.
Go through however many of the steps outlined in this tutorial you need to make it look nice.
Select a nice texture to put in place of the white background. Open the texture, select all, and copy. Paste it into a new layer behind your main one in the icon.
Now we want to mess around with the texture, so take some other textures, drop them on top of the texture layer, and put them on soft light.
You can also put another of those layers on top of it set to Screen and adjust its opacity as necessary.
Now drop a gradient layer on top of the whole thing (not just the background layers).
Set it to soft light.