Skills Required

Confidence comes from Attitude.Before attempting anything one should have confidence that the task ahead is accomplishable,executable and achievable.When we start the work doubting the success,having lot of suspicious about the outcome,we can confidently conclude that the result would be negative.
If you are not confident about your driving you are bound to make accidents.
If you are not sure of your swimming skills you are going to drown.
Here the outcome is not certain,it may or may not happen.But without confidence the negative result is certain.

Physical preparation for an interview is again a two fold.
General grooming of an individual without having any idea of an interview is the first part while Specific grooming few days and few hours before the actual interview is the later part.