Friday the 13th was first recorded as being an "unlucky" day in 1869, when the biography of Gioachino Rossini was published.
Considerations from the Knights Templar roundup, Christ being crucified on a Friday, and numerology (triskaidekaphobia - fear of the number 13, etc.) all contribute to the superstition surrounding Friday the 13th.
Personally, I don't believe in luck. "The footsteps of the righteous are directed by God." To me, any Friday, any 13th of any month, the 15th of March (the "Ides of March"), or any combination thereof is just another day to wake up praising God.
Yesterday is gone, and there's nothing we can do about it. Tomorrow is promised to no one. Every day we're given is a gift, that's why it's called "the present."
P.S.: In some cultures, it is Tuesday the 13th or Friday the 17th that's considered unlucky.