0) Decide early on that you want to apply for a competitive specialty so that you strive to ace Step 1 and your clerkship grades.
1) Rock USMLE Step 1 (visit
http://www.matchapplicants.com for
unofficial program-specific stats in competitive specialties). If you don't rock it, you can improve with your Step 2 score, but this will only help marginally.
2) Try to do as well as you can during third year clerkships, especially on medicine and surgery. Aim to be in the first quartile of your class, but being in the top half of your class is also acceptable.
3) Research during summer in b/w first and second yrs. For bonus points, you can also do research later on if you so desire. Try to get something out of it...pubs, abstracts, posters, etc...and of course a LOR (see 5)
4) Tons of leadership in extracurriculars...bonus points if you can secure regional or national positions (this can help secure more awards, see 9). Try to figure out what you might want to specialize in early on, then target extracurricular activities that are related to your future specialty which you can then write about in your personal statement (see 6)
5) Strong letters of rec...from research mentor, etc.
6) Interesting personal statement that will focus on what makes you unique and committed to your specialty and make the program director want to meet you
7) 1-2 away electives, preferably in the dept of the program director
8) Gather any awards you can if possible (AOA, humanism awards, etc.)...though it's not the end of the world if you don't get AOA
9) Apply REALLY broadly (as many as 40+ programs for some competitive specialties...consult your program director or mentor if necessary). Express interest during interview season by e-mailing program directors if you don't get interviews at first.
10) Reread everything listed above in 9 again.