Select the breeding pair to complement one-another. If one has a weak area, the other should be very strong in that area. But keep in mind that the inheritance of traits is highly complex.
Think about height in people; having a tall parent increases the likelihood of having a tall child, but it is no guarantee. Be honest with yourself as well. If your dog has a serious weakness, such as a temperament issue or hip dysplasia, simply breeding to a dog without this problem will not prevent the trait from being passed on to the puppies.
This is where experience is invaluable. Talking with long-time breeders will help you to learn the likelihood that a trait may be offset, or which breeding pairs tend to create puppies with a certain trait.
Another helpful tool is pedigree analysis. People who are trained in this can determine the degree of relatedness between any two registered individuals, and can even follow the inheritance of certain traits throughout the generations.
Breeding to emphasize a certain trait often involves breeding a dog to a relative in order to solidify the trait. This is termed “back breeding” or “line breeding”, and is a type of inbreeding. Done carefully, it maximizes the positive and minimizes the negative. Done without care, undesirable traits can be spread rapidly through a breed. Pedigree analysis can be very helpful in this assessment.