Without a doubt, the two most important factors are GPA (science and overall) and MCAT score. Many medical schools do not even consider applicants whose GPA and MCAT scores fall well below their averages. To learn more about what GPA is expected, read What GPA do you need for medical school?
Other important factors are letters of recommendations, personal statements, and extracurricular activities.
There are also factors that students have no control over. These factors include race/ethnicity, socio-economic status, citizenship status, and state residency.
Lastly, it is important to note that these factors are most important in determining whether an applicant gets invited to an interview at a medical school. Medical schools only give interviews to applicants who they believe are highly qualified. Once invited to the interview, an applicant’s performance at the interview seems to be the most important factor that affects admissions.