Everyone cracks eggs in their own way, some more effective than others at limiting the amount of shell in the mix. If you crack an egg on a flat surface such as the table or counter-top, you'll be able to open the shell without losing bits of it in the bowl.
Why? Well ... when a shell is cracked on a pointed surface like the edge of a bowl, both shell and membrane are broken, often allowing bits of shell to break loose. By cracking on a flat surface, only the shell breaks, leaving the membrane intact for you to gently prize apart with your fingers. The key is to use enough force to crack the sell sufficiently, but not so much that the egg breaks in your hand. Try it ... After a few attempts you'll be cracking like a pro!