I tend not to worry about things. I have too many high-stress things that I do so if I worried about them all the time I'd probably go insane.
What I generally do is itemize what I have to do, and just be cognizant of what needs to be done. That way I remember what I need to do but I'm not concerning myself with all the possible outcomes, just what outcome I want to come out of it, and what I need to do to get it that outcome.
Don't get me wrong I still get butterfly's in my stomach before I do something big, but it generally doesn't keep me awake at night.