Even if your only knowledge of fantasy is The Lord of the Rings movie, I think you'll find this book really funny to read. And that is a bit odd because it is organized like a dictionary, but I read it front to back occassionally stopping because I couldn't breathe as I was laughing so hard.
A small taste of what's inside:
CLOTHING. Although this varies from place to place, there are two absolute rules:
1. Apart from ROBES, no garment thicker than a SHIRT ever has sleeves.
2. No one ever wears SOCKS.
See also CLOAKS, COSTUME, and KNITTING.
The Tough Guide to Fantasyland by Diana Wynne Jones; put it on your books to buy list.