The difference in a good bird and a show stopper is often feather texture. Feather texture gives the bird a competitive edge that makes it stand out among good birds!
Feather texture varies from feathers that are fine (thin) to coarse (wide) and greatly effects the way the feathers lay against the body.
Begin by identifying your birds plus and minus characteristics as compare to the show standard. Male birds typically lose confirmation when they come into breeding condition and instead of its beautiful show shape becomes long and tubular looking. So you need to asses males especially before they come into breeding condition.
First divide them into buff or yellow feathering as a buff feathered bird should be bred to a yellow feathered bird and then consider the other feather variables giving preference next to feather length. If two birds have the same undesirable characteristic do not breed them together!
Breeding two birds that look just like the show standard usually results in lesser quality birds. Instead breeding is somewhat like painting. If you want to make a certain color of paint, you look at what you have and create it by blending opposites. The worst thing a breeder can do is cull birds that have any overly strong in one area and weak in another just because it is not "show quality". This could be just the stock bird you need to produce that show stopper.
For more information check out Learning & Sharing Article by Brian Johansen on this blog post Oct. 29, 2009 and Tony Ruiz and Ian Mesley articles Yorshires Champion, Breeder & Exhibitor Articles www.yorkshirecanary.com/article.htm