Learn how to turn even the sweetest, most innocent-looking subjects into vampires :)
Crop and prepare your base in whatever way you normally do. For this tutorial, I duplicated the base twice, set the first layer to Screen 35%, and Desaturated the second layer and set it to Soft Light 100%. I then duplicated the Soft Light layer once, and tweaked the Curves. For a tutorial on Cruves, just look/ask around... there are lots, and it's really a cool tool to know how to use.
Use the Dodge tool on the eyes... just enough to make them bright, but not so much that they're super-light. Create a new layer, keep it at Normal, and use a small round brush to paint white onto all areas where skin is showing (face, neck, etc). You might want to do this before you resize if your subject is very small. Find the Opacity bar on your Layer menu, and decrease the Opacity of the white skin layer until it's between 20-40%, depending on how pale you want your subject to be. Erase over the eyes, eyebrows, and lips to make sure they remain well defined.
Create another new layer, set it to Soft Light 100%, and use a dark brown (I used #2b211c) to paint over the hair. Use the Eraser tool to sculpt the color if it goes astray. After you've darkened up the hair this way, duplicate the hair layer, desaturate it (Shift+Ctrl+U) and decrease the opacity to your liking (mine's at 55%). So, to recap so far, you should have one skin layer set to Normal 20-40%, one hair layer in dark brown set to Soft Light 100%, and one desaturated hair layer at around Soft Light 55%. Note: If your subject already has dark hair, you may not even need to do this step.
Create yourself another new layer, and set it to Overlay 100%. Pick a bright red, and with a small round brush, paint red over the eyes so that they glow red. Select another, darker red, and color over the lips, and lightly brush over the apples of the cheeks. If the cheeks come out too red, decrease your brush opacity and try again. Now select a dark gray, and trace around the eyes and eyebrows, and run it over the eyelids to make them look smudged and smokey. You can also run the gray over any bright jewelry to make it darker/grayer.
Create yet another new layer and leave it set to Normal. Right-click on your Paintbrush tool, and select the Pencil tool instead. Zoom in to your subject's mouth, and use a 1px pencil in a slight pinkish-white or grayish-white color to draw in a few pixels to look like teeth, as I have below. Don't use pure white; it tends to look too fake. You only need a few pixels to give the effect, so don't overdo it. It'll probably take you a few tries to get it to look right. Be sure to zoom out so you can make sure your drawn-on teeth look okay. You can fade the opacity of the layer a little if they're too bright. I know they look kind of fake-ish, but odds are people aren't going to study the icon closely enough to notice that the teeth don't look very real.
For good measure, if you choose, tweak the Curves (Ctrl+M) a little bit again to bring in more red or blue... the goal is to make your subject look slightly bluish and pale without losing the red coloring.
Add brushes and text of your choice, and you're done. The border brush below was made by me.
If you'd like to add an extra effect, you can go with neck puncture-wounds. Create a new layer, set it to Color Burn 100%, select a medium-dark red, and use a small, soft round brush to draw in two circles as I have below. Next, use the Smudge tool to smudge the red down the neck to look like smeared blood. If you'd like the effect to be darker, duplicate the bite-mark layer, or flatten the image and run over with with the Burn tool. Create one more new layer, and select a rough chalk or spray-paint brush that's about the same size as the bite marks you've made. Set the layer to Color Burn 100%, and stamp on the rough brush in a dark gray.
And that's it. Experiment and enjoy :)