According to Jacques Pepin. Crack the egg on a flat surface. Don't crack it on the edge of a dish, or pot or any edged vessel. The reason for this is that if you crack it on an edge, the shell of the egg will push inside the egg and bring with it harmful bacteria. I've never heard of anyone becoming ill by cracking on an edge. I've always cracked an egg on a flat surface anyway.
Rachael Ray also gave a tip: if you have a bit of a shell in your cracked eggs, instead of trying to fish it out with your finger, just take a bigger piece of shell and dunk it onto the bit of shell in the cracked eggs. Apparently the two attract.