Some people use an egg separator (a plastic device that lets the white through and keeps the yolk) while others use their hands. Here's another way you might find useful.
Break an egg into a shallow dish. Get a clean, empty plastic bottle and remove the lid. Squeeze the bottle to expel air, then place bottle opening over the yolk of the egg. Stop squeezing the bottle, and the yolk will be sucked up into the bottle. Hold bottle over a small bowl and squeeze bottle to expel yolk.
Mary Berry on Great British Bake-Off Masterclass, BBC2 October 2014.
