Magic in our world is all about balance, sacrifice and community. While the magic itself has no real marked cause or purpose (with some races believing it to be a gift to them from the Gods, and other races shunning those who turn to magic entirely), it is used on a widespread level for a number of reasons. Thus, there are a few rules to make note of behind magic use.
Hard Magic vs Soft Magic
Hard Magic is defined by having rules and laws behind it, while soft magic is the concept that, there is magic in this world and yet it isn't used to solve our problems, people still have to do that. Our world and setting is somewhere in the middle. We shouldn't be using magic as the lynchpin to solving major plot issues, yet it can help support our characters. More often than not, especially in the beginning because these are characters still getting used to the fact that magic has returned, magic is still being understood. Despite the fact that it began to return some 20 years ago (some might even argue about 60 years ago, when the Fifth Age began), it has only become more widespread recently. Before magic left the world, there were institutions in palce to study magic (still used to this day more than ever) but this magic is different than that of the old world. To that degree there are unintended results, and the ability to make things a little wackyshack.
BALANCE IS KEY
In our magic system, everything falls on a scale of balance. For every action there is some sort of consequence or sacrifice. If a character goes into a meditative state to harness his or her abilities, the outcome should involve some sort of draining of his or her life force. Especially if he or she is new to said magic. A period of time should be waited before magic is attempted again because either A. there is literally no power left, no gas in the car so to speak, or B. any further damage to their body may break it for good.
Additonally, the concept that nothing new can be created should exist. For example: Using geomancy to raise some huge earthen gollum from the ground to go take out the enemies, will create a massive sink hole a few miles away and potentially harm those intended to be saved.
The results of using magic may vary. Sometimes there are unintended results: Raining fire balls on the enemy could cause a forest fire. Playfully making waves to tease your pirate boyfriend could create a tidal wave that floods a coastal town. Sometimes those results are things we should have seen coming: You really shouldn't harness lightning while wearing iron plated armor. Sometimes human error gets involved: You really should have read that spell through once before you repeated it, then maybe he wouldn't be a rabbit. And other times magic does exactly what you expect of it.
REMEMBER
While magic here includes abilities waking up within the characters, it should be noted that in order to really harness the power of magic, one should have some sort of tool. Runes, magical objects, spells, potions, are all very important and at play. Magic exists in many objects naturally but can also be enchanted or enhanced by the use of various practices. After all, the Elves cultivated schools for many years. Though now things aren't going as they expect, they are still busily studying.
PRAYER: Meditation, Chaos, Ritual, Incantation, Supernatural
Meditative Magic, in which a person simply uses him or herself as a way to harness energy by entering a meditative state.
Chaos and Ritual Magic, where a specific task is performed to enter a magical state or summon magic, like repeating words, snorting pixie dust, performing a rain dance, etc. Chaos Magic sees the person performing said task in a mind altered state, chanting, taking drugs, etc. Ritual Magic is much more controlled and almost religious, in which some sort of sacrifice and task sets things into motion -- still may include a mind altered state.
Incantation is a charm or spell created using words spoken aloud, or even changed or sung. It is used with the intention of casting a spell on an object or a person.
Supernatural Magic - the abilities to read minds, use telekinesis, see the future, and so on, also fall under this category.
Symbol Magic uses writing and symbols to turn objects and people into more than they seem on the surface. Runes, weapons, hidden doors, etc, can all fall under this category. Through words and symbols, objects take on greater physical quality.
Herbal Magic is a similar concept, only it is ingredient-based. A single ingredient, a power element in the world, may be enough to suffice, but it usually requires some kind of concoction. This may not be a witch with a cauldron, but the use of naturally occuring items to create an outcome; An herb that can cure an illness, ingredients from the far corners of the earth to create a love spell, etc.
Binding Magic is simply the concept that magic binds everything and can be used to create curses or spells, from one person to another.
Sympathetic Magic is similar, only it requires an idol or object that is either in the likeness of a person in question or belonged to them. The idea is then that whatever magic is done to said object can be equally transferred to this person. Another idea would include enchanting an object and giving it to a person as a gift, etc.
Alchemy is the practice of using elements to create profound power, for example the fabled philosopher's stone, the ability to transmute base metals into noble metals, and the development of potions such as an elixer of life.
SPIRIT: Elemental, Invocation, Necromancy
Elemtnal Magic is the act of summoning the four naturally occuring elements. Air, earth, fire and water can all be summoned, in the form of massive storms, tidal waves, lightning to literally strike an enemy down. Or on a smaller scale, like lighting a candle or snowing indoors, though all actions have an equal reaction. Mostly it is defined by the ability to use the elements and manipulate them at one's will.
Invocation is calling on or invoking the spirits. Often times resulting in a possession or conjuring of something otherworldly. This can also be practiced in the practitioner self identifying particular qualities that they are invoking, such as the allure of Aphrodite or the ferocity of Kali.
Necromancy can occur when one simply uses the dead for the purpose of manipulation, most often raised from the ground in order to reveal secret information or some sort of future event. Being aided in occultism or some form of ritualistic magic, not just the spirits but the bodies of the dead can be raised from the ground for many purposes. More often than not, the addiction of darker magic will lead to the use of the dead at the command of the necromancer. THis powerful magic should not be messed with.