I was speaking with a PR tutor yesterday who gave me some valuable insight into the GMAT scoring. Wanted to share.
She mentioned that during her last GMAT, her objective was to determine the importance of the first 12 questions on each section. What she did was to answer the first 12 correctly (she is typically a 780 scorer) and then alternate the remaining questions by answering one correctly and intentionally answering the next wrong. After doing this, she ended up with a 720.
This really illustrates the huge significance of the first 12 questions.