I know that it isn't quite the New Year yet, and actually it's still a while away, however one of my resolutions for this coming year will be to say "yes" more. I realize that in the last year, I have said "no" more often than I would have liked to and I hope to change that this next year.
There are certain situations that warrant a good, solid "No!", but as Tina Fey says, if you say yes, you'll figure it out afterwards.