1. It was general belief that witches were associated with bats and that if someone spotted a bat, it was considered bad luck.
2. Another superstition was that they thought horses repelled witches; therefore, witches rode brooms or pitchforks instead.
3. If a child rode on the back of a bear, he or she would be protected from whooping cough.
4. The lucky horseshoe came from the belief that horses repelled witches. They would hang horseshoes that were removed naturally in such a way that the curved part was facing downward so the luck would not “spill out”.
5. Halloween was originally the ‘festival of hallowtide’ or All Hallows or All Saints day. On these days, the dead souls could enter heaven.
6. The Jack-o-lantern originated because there was a tale that a man, Jack, could not enter heaven because he was a miser but could not enter hell because he constantly played tricks on the devil, therefore, he was forced to roam the earth eternally. He only had a hollowed turnip with a lit candle in it.
7. The reason spilling salt was considered bad luck was because back then, salt was very expensive and was thought to have had healing powers so spilling it was avoided at all costs. If this did happen, however, they had to throw it over their left shoulder into the eyes of any evil spirit waiting to make them ill.
8. The myth that breaking a mirror can bring 7 years of bad luck came from the belief that the reflection in a mirror was actually the image of your soul and broken glass represented a broken soul. One must wait 7 hours before picking up the broken pieces and burying them in the moonlight.
9. For those who could read, lists of “evil days” were printed in almanacs. On these days people would refrain from travelling because those who did would become ill or not come back.
10. There were evil Mondays. The evil Mondays were the first Monday of april, the second Monday of August, and the last Monday in December.
11. The reason why people said “god bless you” was because when they opened their mouth while sneezing, it gave the devil an opportunity to enter the body and saying god bless you counteracted that.
12. Some would touch a man before his execution for good luck while it was also believed that the right hand of an executed prisoner had the power to heal.
13. Black cats were a bad sign because the color black was associated with witchcraft. Because of their fear of these cats, they killed them and caused an increase in rats and mice which eventually lead to the Black plague (bubonic).
14. Ladders were associated with executions so it was considered bad luck to walk underneath one.
15. The superstition of crossing your fingers sprouted because it made the sign of the Christian faith and evil spirits would be prevented from destroying our chances of good fortune.
16. Sparrows are thought to carry the souls of the dead and it is believed to bring bad luck if you kill one.
17. The number 13 was considered unlucky because Judas, the betrayer of Jesus, made 13 at the table. Others pointed out that "the Jews murmured 13 times against God in the exodus from Egypt.
18. If a bird flies through your house, it indicates important news. If it can't get out, the news will be death.
19. The evil eye is the name for a sickness transmitted -- usually without intention -- by someone who is envious, jealous, or covetous. It is also called the invidious eye and the envious eye
20. The evil eye belief is that a person can harm you, your children, your livestock, or your fruit trees, by looking at them with envy and praising them.
Source: http://www.helium.com/items/1612162-superstitions-of-medieval-england