In these of unleaded fuel, you may use spark plugs until the electrode erodes away. Every-so-often, check the center electrode for a sharp edge. As slowly rounds off, file it sharp.
Admissions officers look first at test scores, the rigor of the courses you take, and your grades in those courses. After that, they are interested in a student's extracurricular activities -- in other words, how you spend your time outside of classes.
At the same time, keep in mind that Stanford has holistic admissions -- the admissions officers will be looking for students who will bring more than good grades and standardized test scores to their campus.