The Zombie Project
Why Zombies? Because we love zombies. They're everywhere. Sometimes we, ourselves, are zombies at least until third period begins or until we've had our coffee, whichever comes first.
This is also a good way to learn non-destructive editing techniques, playing with layer adjustments, importing source images as layers, and working with clipping and layer masks.
Here is a tutorial on how to ZOMBIFY yourself. Consider it a starting point, not an end-point-- you're free to incorporate other techniques above and beyond what this artist demonstrates.
Brushes for almost any effect (smoke, fog, blood, etc.) can be found at brusheezy.com
If you like to listen to music while you work, here's a suggested soundtrack