I am one of two members of the Field Force in my Congressional District. We both do the official West Point interviews in this District. To date each of us have done 10+ interviews in the last month. In this district we have about 50 candidates for two slots. If you went to SLS and got an interview there, you do not need to get an additional interview by the Field Force. If you have not been contacted by a Field Force person you should look in your portal (they are listed there for your District) and contact your local Field Force Rep.
The interview is very important. It is considered a critical event in the admissions process. Do not arrive in jeans and a T-Shirt. Be well groomed. Be prepared to show the Field Force person all the information that makes you a good candidate (class standing, grades, leadership positions, SAT/ACT scores, activities, etc.).
Be positive and be able to show that you REALLY WANT to go to West Point and be able to sincerely answer the question "Why do you want to go to West Point".
Be 15 minutes early - do NOT arrive late. Look the interviewer in the eyes (friendly expression) and shake hands firmly. Be prepared to ask questions to show you have researched West Point. Relax. The interviewer is not trying to trick you but to help you.