Well, this is a pretty big question, perhaps too big for this venue. Each frog species has its own set of preferences (and not all breed in ponds). Frogs generally select sites that have the necessary food and shelter for the tadpoles and not too many predators. However, they often make very bad choices, breeding in small puddles that dry up long before the tadpoles mature or in places loaded with predators. They probably key in mostly on water temperature and flow.
Like many animals, breeding frogs are often clumped. The benefits are the stimulation of mass breeding activity and the relative ease of finding mates.