Black cats are unlucky - this one came from Europe. People believed if a black cat walked passed you, there would be misfortune and death in your life.
When you spill salt, throw salt over your left shoulder - way back in the day, people believed that you're throwing salt in the devil's face.
Don't walk under a ladder- in Egypt, they thought a leaning ladder was in the shape of a triangle and if you walk through it, it would destroy them.
Knocking on wood 3 times (I definitely do this)- originally it was to ward off evil spirits, but some knock on wood 3 times to make sure the faiths don't hear what was said.
Broken mirror caused 7 years of bad luck- this back story is interesting. It came from Greece, people referred to as "mirror seers" would tell fortunes by looking into the other person's reflection. If the mirror was broken, that person was predicted to likely die.
Which superstition do you believe in?