Clean portraits free of clutter seem to be the best. If the dog happens to have a favorite toy or cute behavior, I try to showcase that.

The work Julie does with folks holding the animals is also very effective, partially so because of the celebrity value of the people involved.

Typical volunteers holding the animals doesn't usually go all that well. Even worse, there are some rescues that use prisoners on a work-release type basis and they have a lot of photos of the orange jumpsuits holding the dogs.