Preferably show both the males and females.
Welsummers are a rectangular bird with a long, flat back and a fairly deep breast. As with all breeds, handle the birds and chose the birds with good muscling over the breast. As with all laying breeds, look for good handling quality on the hens. That means width between the pubic bones and space between the end of the keel and the pubic bones (this area should be soft and pliable, without a heavy fat pad.) The keel should be long and the body should be deep. The back should be wide. All of this is best judged with your hands.
Welsummers should have a long neck and tail. Their tail is higher than most breeds. I'm noticing a mistake in the APA Standard so I went to the bantam. The tail should be at a 60 degree angle males and 50 in females. The tail is long, and unlike in many breeds, it is only slightly spread.
The plumage should be tight and waxy, not fluffy like many other breeds.
Welsummer males have black breasts with red mottling, and their hackle is a deep orange color free from any black striping.
All Welsummer females have straw-colored shafting. This is in my experience easy to achieve. What you really need to work to obtain is black stippling evenly distributed over each deep reddish brown feather. Many birds will have too much red on their shoulders with not enough brown and black. Others will have too much black and instead of fine stippling you get black blotchiness on the feathers.