If you use a standard grater to shred potatoes, you've probably scraped your knuckles or fingers on occasion. Instructables suggests using a fork to hold the potato.
When shredding, stick a fork a centimetre or so into the potato. Use the fork to hold to potato and shred until the tines of the fork begin catch on the grater. Then, rotate the fork and make the grater parallel with the fork for the last bit of potato. This trick also works for onions (and probably other vegetables too).
Finger-Safe Potato Shredding [Instructables]