While everyone here has some great advice for this, and while a lot of it is mechanical let alone methodical, think also about it this way.
While some are saying to take the score out of it (again, GREAT ADVICE and I am not criticizing that), but also, take the entire tournament out of the picture.
What I mean by that is - and this works for no matter the tournament or the venue - is to treat it like it is any other set or pair of lanes that you would bowl on. When you really get down to it: The stadium, South Point, Woodland Bowl, Fountain Bowl, or Northrock Lanes is no different than Strike'n'Spare Lanes in St. Charles, Missouri, or Paris Bowl in Paris, Texas. You're down to the same 60 feet of lane that everyone else bowls on.
What I mean here is that you may be letting the actual event itself get you stuck in Analysis Paralysis. We get it; big tournaments like this can be overwhelming, and I'd venture to say that 100% of us have had that feeling and then some at one time or another. But once you get down on the lanes, think of it like a practice session, open bowling, or league at the best. You get your mind into that normal mindset/zone that you would be for league, and then let the mechanics and processes others posted about take over.
With that will come experience on how to handle the atmosphere of a big tournament, and you'll come out better regardless of what your scores tell you. Just settle in, don't let the moment overwhelm you, and you'll be fine.
BL.