The process of selecting a yearling is a two-fold exercise. Firstly the BREEDING needs to be taken into consideration. The mare is as important as the sire, if not more so, e.g. if a mare has had 6 foals (5 runners, 1 winner) your chance of buying a bad horse is pretty good, but if a mare has had 6 foals (5 runners, 5 winners), 100% run/win strike rate, your chance of buying a winner is far better. Black type mares (feature winners / placed mares) are better but not essential.
Secondly, a horse's CONFORMATION is vital to the selection process. The BIGGEST and most important common denominator in ALL good horses is the length from the hip to the hock (see diagram) and the length from the elbow to the knee. These are lengths of an arc, which make the stride bigger or smaller. "A horse must have a good, wide airway, big honest eyes, good feet, which land squarely and a good length of rein."