If I remember correctly, I applied unsharp mask with amount 20, radius 40, this increases the contrast, then one more unsharp mask with amount 60 or 70 and radius 1 for sharpness. The tonal values were then changed further by the tritone, but that is easy to experiment with when you load different tritones with preview turned on.
The result obviously still lacks quality, any adjustments are best done on the file right as it came from the camera or scanner, and the sharpening should come in several steps as you downsize the file.
Effie, this is really cute but needs to be sharper, also increased contrast would help as right now the tones are flat. Here's what I mean (the tritone is just for fun)