Allison in our Irvine office unearthed this from Bucknell University's web page, What "Looks Good" to Medical Schools? The particular piece of advice is spot on for any student preparing for college, whether or not you want to be a doctor.
5. "Walk on water and have someone see you do it" — Do something you love,
make a difference that is valued by others. Whatever your strengths are
(leadership, initiative, perseverance, compassion, attention to detail,
competence, cooperation, critical thinking/good judgement, etc.) need
to be documented. This can be done in volunteer work, in sports, in
clubs, in summer jobs, in internships, in research, … in just about
anything. Put yourself for a significant amount of time in an
environment you love where you can make use of your personal strengths
and be observed by some "authority" who can, in turn, write a strong
letter for you. You will not be able to predict what you will do that
will impress the "authority," but if you are doing what you like to do,
and if it is worth while, and if you do it with enthusiasm and
competence, the "authority" is likely to see it. Yes, doing this in an
academic (research) OR medically related arena is good, but doing it is
more important than where you do it. Doing research poorly, doing
volunteer work reluctantly, or working incompetently would NOT help. It
is not so much that you "check a box" but that you "make a difference."