What are the major evolutionary trends that developed among major vertebrate groups, specifically those that allowed for the transition from aquatic to terrestrial life?

Development of jaws in fishes for catching their preys, which previously did it by rubbing and sucking.
Development of lungs and limbs for surviving on land. Animals were aquatic previously, and in order to survive on the land, they required lungs to breathe and limbs to move. 
Development of processes for regulation of body temperature in order to survive the extreme climate. Thick fur coats in animals, is an example. 
Reduction in the number of teeth is also a major evolutionary trend, and development of specialized teeth for different functions of chewing and cutting also helped invertebrates.