A lot of my Christmas gifts were tied to my upcoming trip to Mexico City. Among the least costly but most useful has been a book of Spanish slang, expressions and grammar rules, tied specifically to Mexico.
I'm trying to attack the book one section at a time. Some of it is review but probably an equal portion contains idioms and customs with which I'm entirely unfamiliar. For example: No son enchiladas literally means "they aren't enchiladas," but it really means that something is not as simple as suspected. Like, I'll take care of it, but it's not like making enchiladas, so it might take a while.
One other thing I've known for a long time, but which I was reminded of, is the se me phenomenon. The verb "to forget" in Spanish is reflexive: olvidarse. If I forget to bring my book to class, I don't say olvidé mi libro. Instead, I say se me olvidó el libro. The subject of the verb is the book (it's the same if you drop or spill something -- caerse). I'm really saying that the book forgot itself of me, or the book was forgotten by me. It's still understood that I'm the dick who forgot the book, but it's not so harsh. The accidental aspect of the situation is emphasized. Blame-shifting FTW!