Any special needs they may have ie medication, excessive attachment with the owners, anxiety (for the smaller dogs) and whether they are friendly with other animals. It is also helpful to know what sort of training they've had, to gauge whether letting them off their leash to play fetch is an option. And of course any relevant information the owner has on their pet. I've found there are little things and personality traits that a sitter wouldn't pick up on without previously being told by the owner.

I don't believe in taking dogs to those tiny fenced in dog parks, I would take them on runs, walks, playing fetch in more opan spaces. One of those open spaces being my own apartment grounds (it's actually quite nice)