I agree you need to develop a pre-shot routine. Having one keys the
subconscience that it is time to bowl and what your body has to do.
We use the conscience mind to train the subconscience mind to operate
automatically complex bodily functions with only a few key triggers.
Think about how you had to learn something really complex like typing
or operating an automobile. You had to think about it at the time with your
conscience mind and train your subconscience so that now, you don't have to do any real thinking to perform those complex operations. Your body can do them
with only minimum conscience effort.
Same thing with bowling. You want to get to the point where with
only a few key triggers, your body will operate automatically. A
pre-shot bowling routine is one key trigger. The less you can think
and get in the way of your subconscience mind, the better. Your
pre-shot routine is a way of clearing the mind of unimportant or
distracting thoughts.
Someone else mentioned this and it is important. Only use positive
triggers. The subconscience does not recognize the word 'not'. So
if you think "do not pull this shot", it keys on "do pull this shot",
which is why many bowlers who try not to do something will end up
doing it anyways.
Better to use something like "loose armswing"
or "roll the ball".
A pre-shot routine that also involves taking a deep breath or two and
slowly exhaling as you start seems to help too in helping to keep the
muscles loose. If you can do the same things all the time and keep
the mind clear except for your keys, then pressure shots will be
treated as just a normal shot.
Edited to add:
The conscience mind is more deliberate and slower. You use it to train your
muscles to perform actions. Once you have trained those muscles, they operate automatically and faster by way of the subconscience mind. When you first learn something and use the conscience mind, your actions are slower and clumsy. With
the subconscience mind those actions are faster and smoother.