This video has a number of good points. If you're in a hurry (which you probably are because you're hungry) watch the first 59 seconds where she describes slicing the onion in half and peeling it, then fast forward to 2:44 and watch that section on slicing through 4:05. It always helps to have a sharp knife. When holding the onion, keep your fingers bent so that your knuckles stick out past your finger tips ("the claw hand") and let the blade of the knife ride against that protruding first knuckle. That will save your fingertips from the sharp edge of the knife. Watch her style so you can avoid the band aids.