You should write a clear and detailed description of the academic program you want to pursue. You should clearly identify the area(s) within your field of study in which you want to specialize in or concentrate. If there is a specific research project you wish to undertake, you should describe how you intend to meet your goals. You should outline why you need to go to the particular country and institution and how this will enhance your knowledge, skills, and understanding in the discipline.
Candidates applying for non-degree admission or for a visiting researcher affiliation (mentored pre-doctoral research-only program) should be especially clear about their study/research objectives and what they hope to accomplish in the United States, as non-degree admission policies or visiting researcher affiliation vary considerably from university to university and often from one department to another within the same institution. Access to course work, faculty time, and university facilities may be defined differently in individual cases and priority may be given to degree candidates.