Below are some excerpts from The Magical Society: Ecology & Culture. The author's could literally take up an entire chapter on magic and fictional worlds -they very nearly did- and there is a lot more in the book, but these may very well give you a guideline, or even a jumping off point.

For every magical planet, there are dozens of non-magical ones (like our base planet), yet the multiverse demands certain constants. Despite the discrepancy of available magical resources, basic catalytic processes (like adaption, natural selection, and evolution) shape life on the most magical planes and even affect how life interacts with the body magic. Though some gladly expend vast amounts of magic to see the world of their imagination, remember that every action has an equal and opposite reaction, even with the body magic. Our reach and power are orders of magnitude greater than mortal magic practitioners, and we are capable of creating greater magical reactions upon ourselves. As gods we must always be aware of the magic budget in the material plane, build our worlds with as little magic necessary for its survival, and learn to always ration our power. In a sense, even gods must adapt to their environments or die.
Magic is the greatest force in the multiverse, and the only thing comparable to its pervasiveness is light. Light is everywhere in the universe, and only within solid bodies is light excluded. Unlike light, magic permeates everything. It is a critical building block of the multiverse, and even nothingness’ main component is magic. Even vacuums are made of magic. Although everything is made with some magic components, magic, as the ability to use powers or spells to alter reality, isn’t available everywhere. Some places have very low levels of magic, in which the typical functioning of magic can’t occur. But even these places have some magic, just infinitesimally small amounts. Unlike other planetary energy sources, magic is alive and sentient with a will of its own. Magic is the body of a massive entity, and the rest of existence depends on it functioning properly. It is almost as if the multiverse is some sort of parasite on a giant magical creature. Magical energy permeates everything on a planet, but it is not a static force. Unlike matter, which always seeks an even distribution state (entropy), magic always seeks an uneven distribution state. To think of it in other terms, matter is by nature lawful while magic is by nature chaotic, although this is a hotly debated topic among the gods. Magic is always moving, either through ley lines or magical topology, and it strongly resists being chained to a single place. It is this resistance to stability that makes preparing arcane spells so arduous and the production of magical artifacts so draining. But there is much to discuss before the inner workings of magic.
Unsurprisingly, magic on a planetary scale is a complex thing. Magic works very similarly to water in that it flows along the path of least resistance. It pools anywhere, regardless of depth, height, or pressure. Unlike water, magic doesn’t usually pool in vast quantities. It is rare to find a magic pool any bigger than a large pond. A magic “stream” is called a ley line, and a magic “pond” is called a terminus. There isn’t any relationship between the amount of magic flowing into a terminus and the size of a terminus; some of the most powerful ley lines have small termini while weak ley lines may have large ones. Ley lines are also unusually straight compared to most water streams. Most ley lines are divinely aligned, and most termini are arcanely aligned, though some ley lines and termini are aligned to both. Unfortunately for many mages, magic is a subtle energy, and magical topography is characteristically more so. Magical topography takes no consideration of physical situation, and it changes with incredible speed in comparison to physical topography. There is no relationship between physical topography and subtle topography (what spell casters call the magical topography). Subtle topography, as best explained to me, is a giant system of tunnels permeating the entirety of a world, completely unaffected by physical matter. I think of these tunnels as veins and arteries in three dimensions with tiny little capillaries filling the entirely of the remaining space.