The Four Great Powers

Fire: Like a magical magnifying glass, the Elemental magician focuses all the loose fire magic floating about into one unified beam of energy. The result of this is a marked increase of heat. Perhaps the object targetted by a weaker Elemental magician will not instantly burst into flames (if combustible), but it will at least acquire a distinctly higher temperature than it should have. A "trick-of-the-trade" in using fire energy is to withhold as much as you can, and then release as much as possible all at once in a concentrated burst-stream.
Air: Air is typically the most used element because of its highly versatile nature. Air can be soft and slow to cool down a tired magician, and conversely it can be raging and concentrated to destroy structures, deflect projectiles or to relocate object forcibly. Air is most often used to make life easier, not as a destructive force. It can be used to cool (or warm, I suppose, depending on the temperature of the air in question) something, to hinder anything airborne, or to create mini-twisters.
Earth: Earth Elemental magic is very odd. The manifestations are extremely varied and radically alter whatever they affect. Earth can be used, in its most powerful form, to cause earthquakes, and in lesser forms to cause ground to cave in, to form spikes, to become uncooperative to an adversary, and virtually anything else a caster can imagine. The trick to using Earth is to combine it with another element. Earth and Wind equals a sandstorm; Earth and Water equals quicksand or mud. Earth and Fire equals hardened clay (which
can be pre-shaped). The drawback of Earth, however is that it is extremely rare to find an Elemental magician who has anything more than passing control of it.
Water: Water is the quietest of the elements, though no less powerful. It can be used to turn dirt into quicksand, to cause whirlpools, to feed dying plantlife, or to kill over-thriving plantlife through deprivation, to cause rain, or even a local flood. Water, though often called "The Element of Life", is also quite capable of ending life if present in inappropriate amounts. Lastly, Water is also used to quench fires.