Danielle has written a great slide telling us about some great superstitions.
Are you writing a romance?How about having the main character give the love interest an orange. It is believed giving someone an orange will make them fall in love with you.
Visited by a strange man?
Did the main character drop a knife? Superstition says if you drop a knife a man will visit. Drop a fork, a woman, and a spoon a child.
Bad luck at the dinner table?
Don't give parsley at the dinner table. Superstition says it will bring bad luck.
These a just a few she mentions. Watch the entire slideshow and add a little spice to your book.
Here are some more links for superstitions:
Superstitions and Their Origins : Psychic Library
20 Things You Didn't Know About... Superstition : Discovery
Understanding local superstitions can help you avoid a faux pas—and maybe improve your luck, too. : TravelandLeasure.com
Enjoy (knocking on wood)!