It's funny how often we assume that a world that is so unlike our own that it magic running rampant will follow the same laws. Sometimes it's done for the sake of clarity (an MMORPG set in a world where the calendar had more or less than 365 days would confuse and annoy us), or for accessibility (imagine if Wizards of the Coast had decided that their Eberron setting had 1/3rd Earth's gravity, or was a few hundred kilometers closer or further from their sun). But still, we often find that there are a few commonly accepted subversions of those laws, that occur in quite a few works. For example:
Terrain that floats above the natural landscape: This is one of my all-time favorites. The imagery of land floating high above our own is one that just seems to stick in our minds, to the point where it occurs even in science fiction, most recently and notably in James Cameron's Avatar. Other past notable examples include the land of Laputa from Jonathan Swift's Gulliver's Travels (a name later used for a similar location in Hayao Miazaki's film Castle in the Sky), Themyscira in the Wonder Woman comics, and the City in the Sky in Legend of Zelda: Twilight Princess.
Sapient wildlife: This one's a given. Think Ents from Tolkien's Lord of the Rings, or Elementals from... well, just about anything. Also in this vein is the Grand Oak from the video game Dragon Age: Origins. Since wildlife can also mean animals, warewolves and other creatures of a similar nature are also included in this category, as well as talking animals. Think Disney's The Fox and the Hound wasn't a fantasy? Now you know.
Disproportionate Strength: Or, "How the hell does Cloud lift that sword?!". This is one of my least favorite subversions. It breaks my immersion in a fantasy world when a beanpole like Cloud Stryfe from Final Fantasy VII can still lift that monstrosity of a sword with one hand. I couldn't even lift a friend's replica with two! Granted, I'm a scrawny girl, not a tall man, but even this friend admitted that he couldn't really lift it either. You'd have to be Arnold freaking Schwarzenegger to lift it like that. And, as I mentioned before, Cloud is certainly not. Moving on.
Magic: I know, right? This one is so common that if a story does not have some sort of magical element in it, it generally isn't fantasy. But Magic in all its forms still takes the laws of the world we live in and shatters them like a pane of glass on Mythbusters. Even in fiction that takes place in our own world, when magic is invoked it instantly becomes almost a different place altogether. Magic can do things that would make most modern physicists have an aneurysm! People fly, matter is created and destroyed, fire springs out of nowhere and burns nothing but the intended target! Magic is the foundation of all fantasy, and it's also the wellspring from which all subversions of the genre originate, generally speaking.
The way to tell when a story really takes place in a different world is if one of the characters walks into a tavern (usually you can stop there but we'll keep going) and says: "I'm a wizard!" and receives a response of either "So what?" or "Teach me!". Also, on some occasions, "Kill him!". But the point is that almost no one would say "I don't believe you!". To the people that inhabit the worlds of fantasy that differ from our own, these deviations from the natural law of our world are as commonplace to them as gravity and the coriolis effect are to us. And because they don't often question it, neither do we.
So here's a trick to try: next time you sit down to write a fantasy novel or run a game of Dungeons and Dragons (or whatever your preferred tabletop RP system happens to be), try changing the way that gravity behaves, or the color of the sky, and see if anyone notices.