The Fundamental Laws of Magic
Magic Requires Form
You cannot affect something that cannot be expressed as a concrete noun. When you think of something, you've fixed it in your mind's eye. It might be a tangible thing like a flower or an intangible thing like the relationship between lovers. But you must be able to conceptualize it. So, a relationship must have soem sort of physical representation to be able to work. Symbolism and metaphor is important!
Vast unspecific concepts, like Economics or Politics cannot be affected directly by Magic. These are not concrete nouns. Systems of operations cannot be affected directly. But, like all things, such systems are composed of component parts which can be affected. So, while you cannot magically change the market price for Carris oil, you can change a specific buyer's recollection of the price, the notation on the price-board, perhaps the relative amount of Carris Oil in current stock…
Conjuring is another subset of this. Conjuring is the creation of a thought-form. To conjure a flower, you are translating a thought-form into a physical form.
Magic Isn't Free
It might be slight: the barest application of Will to bring a pot of water to boil or to change the color of a specific flower. But the greater the magic, the greater the power-drain. Magic is not a free excuse to do something, it is a tool and it takes effort.
Casting world-changing magics will have world-changing consequences. Conjuring a small wind to fan yourself on a hot day is negligible. Conjuring a torrential downpour might be beyond your character's ability to fully conceptualize. But perhaps they could summon a storm by messing with existing weather-systems…
Magic Lasts As Long As it is Powered
Magic lasts only so long as it is properly powered by Will. One might create a magical wall to keep out an invader. But once the wall is no longer powered, the wall will fade. Conjuring permanent things require the use of permanent resources. Creating a permanent golem of Sand requires sand…
Magic Cannot Be Contained Indefinitely
One may create a talisman or fetish, a receptacle for magical energies, perhaps for use in a large ritual. It might be that several smaller ritual are performed to amass the power, that is then stored in talismans that will be consumed during the end-ritual. But it takes magic to store magic, and no magic may be stored indefinitely. Magic Seepage will occur wherein the stored magic will slowly dissipitate out into the world.