The most important thing of all is type. If you have perfect feet, perfect crest & perfect comb, but type is like a modern game or a d'uccle, you will place last every time.
Four toes are easy to correct; single comb is easy to correct; dark skin but red comb is HARD.
Get a copy of the standard and learn what it says about all the traits. Look at photos of birds who place well at shows. Learn to recognize a good bird when you see it.
Get the best quality breeder birds you can--if your parents aren't willing to spend the price of a good breeding pair--ask if they would spend more if it were a birthday or early Christmas present. Ask for extra jobs you can do around the house or for neighbors to earn part of the cost.
For starting, concentrate on one variety--you can add more later if you choose. After type, I would look for the birds with the most silkie feathers: longer, softer feathers, as well as more silkie feathering on the wings, feet and tail, areas that often have more regular feathers.
Every breeder seems to have their own particular thing that they are very picky about. With some it is wings, with others comb, with others toes. What really matters is the whole bird. If you are looking at several, sort of distance yourself and look over them all. Which one jumps out at you and says "I'm a cut above the others!" That's the one you want.