I open up photoshop, set a new page size 24x24 pixels, DPI 72, RGB, Transparent...
I zoom in to the highest it goes, take off the grid snapping, and anti alias on the pencil tool... I draw and colour half the Icon in most cases, copy it and mirror it over, I then use the Colour picker tool and select the colours to one side of the icon and lighten them... Or if I think I can get away with before merging the layers I use the Brightness or contrast tool to change the colour varience... Then merge the layers, save as a PNG... Then most of the time leave that Icon open, or open as a copy and work on the next using parts of the other, or using it as a reference, that's why most of my icons have a nice running theme.
Icon's are by far the easyest things to make... I made 93 of them in about 4 hours combined time...