I would say to a new admissions professional to have a "thick skin". Not every student you meet is right for your school, not every student you meet will enroll at your school and it is not YOU they are not buying into. Keep prospective about what you can resonably manage in one day so that you are not overwhelmed and you can help your students more effectively.

Know your audience.

Both pieces of advice are crucial.  Knowing your audience is helpful because as an admissions representative it is my job to match our students to the program appropriately and not bring up concerns where I see fit.  That is for both the school and the student.  One more piece of advice that can go a long way is to keep your judgements in check.  We dont' know everyone and what their stories are.  How they present themselves can be a completely different story as to who they really are and what they are capable of.