One of those things is squishing two words together when they should remain two words. An example of this I have seen a lot of recently is "everyday". Now before you start yelling at your screen, I realize that "everday" is a real word. However, "everday" is an adjective used to describe a noun. It is not an adverb used to describe the frequency with which an action occurs. So you use "everday" to describe things. "Every day", on the other hand, is used to describe actions.
It is correct to say "everyday people", or "dwarf tossing is an everyday occurrence in Canada". It is not correct to say "I toss dwarves everyday", or "some people shower almost everyday".
A tricky example is a sign in front of a restaurant saying something like "hamburgers, $1.99, everyday". I think this is wrong too, because it implies that hamburgers are that price every day. "Everyday" does not describe the price itself, but the state of the burgers being that price. Although I can't judge the store's sign manager's intentions, I think the lack of grammatical sensitivity is clear enough that they will be destroyed in the upcoming grammar apocalypse.
Now go think of some examples of correct usages of "everday" and "every day", and get back to me tomorrow. This will count toward your final grade.
P.S. Anyone who tells me why the album cover above is there will get a fake internet cookie!