Failing to use insight into self and experiences in the process, particularly essays and interviews.
Responding to essays and interview questions with what the applicant "thinks" the Admissions Committee wants to hear (i.e., assuming there is an "ideal candidate" we seek).
Approaching the application as though each part is a separate entity. We evaluate candidates holistically, based on their overall profile or the picture that emerges from the entire applicaton.
Selecting recommenders who are unable to answer questions we ask on the recommendation form (e.g., academicians/professors are not always able to speak to a candidate's managerial and/or leadership potential).
Lacking focus - unable to articulate career progress to date, as well as plans going forward.
Trying to be all things to all people.
Failing to follow directions (yes, this still happens after high school graduation!)
Including too little/too much information in the application.