Witness preparation is a process in which a witness for a case is prepared to testify by the legal team which intends to call the witness. Not all witnesses are asked to undergo witness preparation, but usually key witnesses are encouraged to work with the legal team. Preparation benefits both the witness and the lawyers, and can make or break a case.
Whether a witness is an experienced expert witness or someone who has never taken the witness stand before, witness preparation can be important. The lawyers are not allowed to coach the witness specifically about what to say on the stand, but they can take the witness through his or her testimony, usually first in a casual setting and later in a mock courtroom, to get the witness comfortable and familiar with the courtroom setting.
During witness preparation, the legal team provides the witness with specific tips and advice about how to behave on the stand, such as recommending that the witness speak clearly, reminding the witness to testify accurately, and telling the witness to avoid using gestures and excessive colloquialisms during testimony. It is also typical for advice to be provided about dress and demeanor so that the witness will be presented in the best possible light.
In addition to walking the witness through testimony and questions from their side, the legal team may also stage a cross-examination. This is used to demonstrate the kind of questions which may be asked by the other side, and to help the witness prepare. Cross-examiners may try to throw the witness off, with the goal of eliciting compromising information or simply undermining credibility in front of the jury. By being prepared for the kinds of questions which will be asked, the witness can practice keeping cool on the stand and responding clearly and in a measured way.
Sometimes the lawyers will record video during witness preparation. The legal team can later take the witness through the video to point out strong and weak points as well as specific issues. For example, wrinkling the forehead or making other facial expressions can be detrimental to credibility. The lawyers can also point out areas where the witness's testimony is clearly confident and strong, to show the witness the demeanor and presentation they are going for.
Witness preparation gets witnesses more comfortable with the witness stand, the courtroom, and the kinds of questions which will be asked. Even with preparation, a witness can still flounder on the stand, especially if she or he was not completely honest with the legal team ahead of time about issues which could be brought up. For example, if a witness thinks that it will be possible to conceal an affair, it's possible that the opposing counsel will dig up enough information on it to make the witness feel uncomfortable on the stand for the purpose of making the witness look questionable to the jury.