Dizzy has a good analogy for most people. Think about what you need to do to execute the shot, the one or two things that most effects your shot. Example, keep my feet slow, stay back of the ball!!!! Those are my two! CONCENTRATION is what helps execution, block out the score and people. I for one in the 10th frame throw the first ball for a strike, look down and walk back to the end of the approach, turn around and focus on the lane. Taking a deep breath also helps some but the preshot ritual is what most bowlers fail to do.
HERE IS A GOOD STORY OF NOT FOCUSING! I throw the first 11 in sanctioned league play, I go through my preshot. Go into my stance, get ready to start my approach and ALL OF A SUDDEN I FEEL A ARM AROUND MY SHOULDER, my best friend who I am bowling with puts his arm around my shoulder and starts telling me a joke!!!!!!!!!!!!!!He had too many beers and just thought it was funny (Good guy just doesn't think sometime) I laugh, step back on the approach and pull the next shot on the nose, 6-7-10 split, 297! Was he wrong for what he did, yes, but I was the one to throw the shot, I lost my focus and should have taken more time. Good news was I had a sanctioned 300 and 299(stone 8)in the previous couple of months. Good Luck its just a matter of time.