Drive and desire, lets see....maybe flip a coin or bring a magic 8 ball, possibly tarrot cards. On the serious note as I hope you already know there are no guarantees in life so a puupy with a lot of young trained wrong could lose it anyways. Some say bring a tennis ball and pick the fastest retrieving one others use duck wings hoping for a birdy pup. Its kind of a go fish thing. You would have to see the pup on multiple days to get a good idea of his attitude.
X2 on This. But like you stated earlier, a titled pedigree stacks the deck in your favor. When you find a litter with a good pedigree and a dam and sire you like, pick the one that pooped last.