1-Knocking on wood
Usually we tap our hand on the wood 3 times so that the bad thing we hear does not happen. With this behavior, we increase our belief that the event will not happen. (But be carefull or you might hurt yourself )
2-Black cats
Generally, in many cultures black cats mean 'bad luck '. In some European communities, black cats are considered common companies of witches . Maybe this belief arise from there. In addition to this , in Turkey when people see black cats they touch their black hair. If they are blonde or anything colour , they touch friend's black hair. So bad luck doesn't come to them . But I have to say that , what's wrong with black ? I mean why is the black cat not white or yellow etc. I think it is racialism.
Look at that, how cute! How could be a bad luck?
3-Trimming Nails at Night
Seemingly it's bad luck to trim your finger or toenails after dark, at least according to superstitions in Turkey, India and South Korea. In Turkey, if you trim your fingers it means your life will shorten. I think I have a meaninful explaining for that. For example if you cut your fingernails in dark it can lose and you can't find it. And it can't be healthy and clean. 4-Friday the 13th According to Christians, the bad luck of Friday the 13th is a belief that stems from the Last Supper of Jesus. Because there were 13 people at the table that night, and one of the apostles had betrayed Jesus. According to another belief; It is said that Adam and Eve were expelled from paradise by eating the forbidden fruit on Friday. Inspite of that, in Turkey friday is a divine day for muslims.
5-Throwing Salt Over Your Shoulder
As superstition says, pouring salt is bad luck and throwing a pinch on your shoulder will reverse this bad luck. It is usually thrown over the left shoulder. We do not know exactly when this custom began, but there are several explanations for why spilled salt is unlucky. Let's look at Leonardo da Vinci's The Last Supper and you'll see Judas Iscariot knocking over salt with his arm. Since Judas cheated Jesus Christ , people started to correlate salt with lies and unfaithfulness. Throwing salt on shoulder also blinds the devil who forces you into bad things.
Finally, I will give some common superstitions in TURKEY.
1-Whatever the pregnant woman looks at while she wants to eat something (crave), the child will look like her.
2-Gum is not chewed in the evening, chewing gum in the evening is dead meat.
3-Hand-to-hand knives bring bad luck. They say it makes a fight.
4-If an owl sings on the roof of a house, it indicates that there will be a funeral in that house.
5-Throwing bread crumbs on the ground and chewing them with their feet brings the abundance of the house.