The only thing scary about most Halloween photos is how bad they are. So this year, try adding a ghoulish mood to your Halloween shots. About.com has several suggestions:
1) Lighting your subject from below can add a spooky glow and interest to the picture. Try using a flashlight under your subject or bouncing your flash off the floor (if you are using an on-camera flash, hold your camera upside down).
2) Add color to your light source. You can do this by using a colored light source, a glow stick, or colored cellophane or gel over your flash.
3) Try some special effects like a fog machine or dry ice (be careful).
4) Make mistakes on purpose: Add movement with slower shutter speeds or use higher ISO’s to add noise or graininess to the picture.