Yeah the LOI like virilep said, get another recommendation from someone who you are currently working with or taking their class....plus sending "Update letters", letters that tell them of something you are currently starting (such as starting to volunteer, shadow, or do research, etc.) or finishing (such as a class you finished and the grade you got, hopefully an A, or you just finished research, etc.), something significant that was not on your AMCAS in the beginning that they should know about....