In my opinion, and it has worked well for this program, I look for HEALTH (vet cleared), TEMPERMENT (I prefer a tad more of an extrovert to an introvert), TRAINABILITY (how easy is the dog to train? How well does dog deal with various environments?),  PLEASABILITY (does the dog genuinely want to make you happy? Does he desire to make you happy even before his own needs and desires?), A GOOD NOSE (does the dog have above average ability to find scent, and does it attract his attention?), STRUCTURE (how well is the dog put together?) and HISTORY (meaning I look at the pedigree of his ancestors).