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.
Many studies of admissions decisions ask colleges and universities what qualities they value (almost always, grades in college preparatory courses rank first), and which they value the most.