Every year our program sit down together in February to go over all the candidates. There are always 10 or so who really stand out with former lives that are extremely impressive (e.g. law degree, PhD in astrophysics, former professional athlete, etc.). These people get ranked highly but I suspect end up at elite institutions. The rest of the field is harder to differentiate. If it were up to me, I would pick people who were interesting, with varied life experiences, and backgrounds in liberal arts/humanities. The people who other residents/attending a tend to favor are folks they know because they have rotated with us. This past year >80% of those who matched did an AI at our program.
Since there's not much you can do at this point to develop a truly impressive resume or have lived an interesting life prior to med school. I'd say that aside from applying broadly, doing AIs at programs you are interested in and have a reasonable chance at matching into is your best bet.