I was "taught" in a foods class to crack an egg by tapping it with a spoon although I prefer tapping it (the fat middle part of the egg) on the counter. (There was some reason given on why you shouldn't do that, but I don't care. :P) I don't recommend tapping against an edge though because less surface area = more force and you'll get shell pieces more easily. It may take some practice to find the right amount of force. You want enough to get a visible crack pattern but not too much that it actually shatters. Then you can use your thumbs to poke gently at the middle and split it open like you're opening a book.