This was done for a "Zombie Walk" in my city, and it was the first time I'd used liquid latex, which was lots of fun. Be sure to watch some tutorials on how to use the latex before you try it! I watched a few different ones. Then, just let your creativity guide you!
NOTE: If you have a latex allergy, or can't afford the stuff, the BEST base I've ever found for zombie makeup is this Mint Mud Mask for the face. http://www.drugstore.com/queen-helene-mint-julep-masque-mint-julep/qxp79218
Not only does it dry in a GREAT pale green color that's a good base for other makeup, but it's actual good for your skin, so your face won't feel all gross at the end of the night when you remove everything!
***Oh! I almost forgot - at the end of the night you're gonna need some serious help getting all this shit off. You can try cold cream, which works OK (you still have to peel off the latex, and that can HURT). You can also use baby oil, or even plain old olive oil, which seems to work very well!
Be sure to start with a nice clean face, and be wearing your about-to-be-messed-up costume clothes when you start. Tie a bandanna around your hairline if need be to keep your hair off your face. (Guys: SHAVE FIRST!)
The first thing to do is, using your makeup sponges, apply some patches of liquid latex to different parts of your face. Avoid eyebrows! I used Krylolan brand liquid latex, un-colored (dries clear). The gently press a single ply scrap of toilet paper into the latex, so it sticks.
Let the first layer dry fully. Then do more layers (letting them dry fully in between) to build up more layers of latex & tissue, wherever you want to end up with flaky, scaly, peeling looking skin. I did 3 I think.
After you have all your latex & tissue applied, do a latex layer all over your face to create a base you can apply makeup over. After this dries, apply all over white cream makeup as a base. You can add patches of a light "skin" colored cream over the white so you don't loo like a stark white flaky clown.
On top of the white/pale base, just be creative with adding dark colors around your eyes (I outlined the whole eye area in a dark greyish black) and wherever looks good. I also did some random patches of greens, blues, & greys. Line your upper eyelids in black for more definition, and for a really creepy effect, line your lower lids (both inner & outer) with red lipliner! Be sure to put makeup over your lips, too.
For your last step, use a toothpick or something similar to make tears or gashes or holes in the TP layers in a few places (until you see your own skin) and in the holes, squish some red makeup or fake blood. Let it trickle out around the "wound." You can also do this around your mouth, nose, etc. Now you're creepy!