When you speak of bad luck, it is said that one should always knock on wood. Also knocking when speaking of good luck apparently helps with having good luck. This is an old Celtic tradition related to belief of wood spirits.
208
There are numerous sailors' superstitions, such as: it is considered bad luck for a ship to set sail on a Friday, to bring anything blue aboard, to stick a knife into the deck, to leave a hatch cover upside-down, to say "pig", or to eat walnuts aboard.
70
Placing keys on a table is considered unlucky. (Sweden)
3
Placing a hat on the bed is, apparently, bad luck. (South Carolina)
9
Before traveling a person should, apparently, sit on their luggage. (Russian)
117
In some parts of England, rum is used to wash a baby's head for good luck.
71
Opening an umbrella indoors is said to result in 21 days of bad luck. Some traditions hold that it is only bad luck if the umbrella is placed over the head of someone while indoors.
75
It's bad luck to leave a house through a different door than the one used to come into it.
143