Start with your base, sharpen, or whatever you usually do to a base.
I thought it was too dark so I duplicated twice and set to screen, but you don't have to unless you want your icon brighter. I also desaturated both duplicates.
Set this by ewanism to lighten 100%.
Set this to screen 100%, and move to wherever you want to on the icon.
Set this by ianthinae to lighten 100%. I erased quite a bit of it.
Set this by ianthinae to lighten 100% and move to wherever it looks good.
Set this by ianthinae to screen 100%. I again, erased a lot of it.
I duplicated the base once, bought it to the top and set to overlay at 60%.
And put a 5 pixel border around it, and leave normal. If you use my example, erase the black.
Any questions please ask.