4-H is truly a great way to get started showing birds. To learn how show quality your birds are, I suggest that you obtain an American Poultry Association Standard of Perfection. This book contains the standards for all APA recognized breeds and varieties of chickens, ducks, geese, turkeys, and guinea fowl. It is a must-have for those wanting to raise and breed show quality birds. It shouldn't be you only tool, however. I recommend attending multiple poultry shows and speaking with fellow breeders or judges. Particularly, I'd advise attending APA sanctioned shows since they nearly always have licensed judges that have been breeding and exhibiting birds on their own for years. While county fairs and local shows are great for teaching youth, they sometimes don't have licensed judges and the birds end up being judged using some obscure standards or just being "pretty". Watch judging and observe the birds that win. Sometimes you can become "barn blind" (miss faults of your own birds or notice the wrong ones) if you don't go out and see other birds from different people.
What makes a bird "show quality" really depends on the bird's specific breed and variety. That's why you should get a Standard of Perfection and talk with other breeders and judges. One particularly important aspect of a show quality bird that I'd like to stress is condition. Condition means few/no missing/broken feathers, all feathers smoothed down (no frayed edges), nails that are not extremely long (judges don't want to get scratched), a neatly trimmed beak, smooth scales on the legs (no scaly leg mites!), good flesh condition, and managable (not flying frantically around the cage when the judge looks at them). If you talk to judges, especially county fair judges, and ask what the three most important parts of a show bird are, you may get the answer "Condition, condition, and condition". Never bring a molty, sick, or neglected bird to a show.
I'd suggest posting photos of your birds in this section for knowledgeable poultry exhibitors/breeders to view and critique. They can give you advice on which birds are more show quality and more likely to fulfill your purposes. It is hard to judge birds just from photos, but obvious faults (poor body type, not enough depth, wrong tail carriage, etc) can usually be determined through photos.
Welcome to the would of poultry exhibition and good luck with your flock! I'd love to help evaluate some of your potential show chickens.
