I know this flies in the face of a lot of common wisdom, but there is a reason that I advised both DDs to not practice for any of their interviews. Just think about the questions they had for the interviewers and focus on being honest and forthright in their responses to questions posed.
I guess it depends on how you define 'practicing', but to me thinking ahead of time of the likely questions that may come up and how you would answer them is part of the preparation you should always do for any interview. If the first time you think about how to answer obvious questions like 'why are you applying to USNA?' it would show a lack of preparation/interest/commitment. Doing research ahead of time about what all is involved in attending USNA and eventually joining the military is something every candidate should do.