What are you excusing yourself from on the grounds that "It'll just be bad luck to do that/ sort that out/ start that on Friday the thirteenth"?
What are you putting off til tomorrow or even Monday?
And what will be your excuse for not doing it then? Lack of time? Lack of funds? Lack of energy? The wrong type of leaves on the line?
If it's important, stop making excuses and do it regardless of the date. Take a risk. Be brilliant.
Just imagine how much better you'll feel for overcoming an obstacle AND that daft superstition.
Good luck! ;-)