When I first look at a horse I asses their pedigree...if there aren't bigger names up front then I kind of don't use the breeding for what they will excel out but at least you can get an idea. If they have the bigger names up close then I'll generally expect them to be that type of horse.
Then I look at their conformation. Then their personality/mind and what they like to do.
I think breeding tends to be a pretty good indicator, if they good horses are closer up, as the good horses get further away I think it won't always be indicative of what they will be good it.
Conformation and the "will" of the horse is extremely important too after you look at the pedigree. Especially the "will/want" part. And for this a horse will normally tell you when you are pushing them to do something they don't want to do.