1). It's unlucky to meet a black cat. 
2). It's lucky to touch wood. We touch; knock on wood, to make something come true. 
3). A horseshoe over the door brings good luck. But the horseshoe needs to be the right way up. The luck runs out of the horseshoe if it is upside down. 
4). It's bad luck to break a mirror. The superstition is supposed to have originated in ancient times, when mirrors were considered to be tools of the gods. 
5). It's unlucky to spill salt. If you do, you must throw some salt over your shoulder to counteract the bad luck. 
6). The number thirteen is unlucky. Friday the thirteenth is a very unlucky day. Friday is considered to be an unlucky day because Jesus was crucified on a Friday.