Here's the method I use for situations where it is important that I do the separation, and the quantity demanded is moderate -- say, up to a dozen eggs. It is possible to purchase liquid yolk and liquid or powdered egg white in commercial quantities, but I rarely need enough to make that worthwhile.
one small bowl to hold the yolk temporarily
one small bowl to hold the egg white temporarily
one larger bowl for all the yolks
one larger bowl for all the whites
For each egg, crack it over your temporary white bowl. Let the white pour out, and then drop the yolk from one half of the eggshell into the yolk bowl. If you are happy with the white bowl, add it to the larger white bowl. If you are happy with the yolk bowl, add it to the larger yolk bowl.
If you are not happy with either bowl, you can try once to get yolk out of white with a spoon. Otherwise, discard it.
Almost every recipe that wants yolks can tolerate some white; few recipes that want egg whites can tolerate visible quantities of yolk.