Most lawyers begin depositions with a series of preliminary questions that vary from lawyer to lawyer, but which generally go something like this:
--Have you ever had your deposition taken before?
--You understand you are under oath?
--And that means sworn to tell the truth?
--And even though we are in an informal setting here in this office, your answers have the same force and effect as if we were in a courtroom with a judge and a jury?
--Are you prepared to answer my questions today?
--There's nothing that will prevent you from giving me your full attention?
--You aren't taking any medications that will prevent you from giving me full, complete, and truthful answers to my questions?
--If you don't understand one of my questions, will you let me know?
--If you need to take a break at any time, tell me, and we'll take a break. Is that okay?
Questions such as these put the deponent at ease right from the start. But more importantly, they'll help you at an evidence deposition or at trial if you need to impeach the witness later with his prior testimony.
Some of the questions cut off avenues that might otherwise be available for backpedaling when the witness tries to change his answer, e.g., "I didn't know I was under oath" or "I didn't understand your question."
In addition, when impeaching the witness with his prior inconsistent testimony, you can use some of these questions as preliminaries to impeachment, e.g., "And at your deposition, you knew you were under oath, didn't you?" . . . "And sworn to tell the truth?" . . . "And you told me you were prepared to give me your full attention?" . . . "And we agreed that if you didn't understand one of my questions, you would let me know?"
The form and style of impeachment varies from lawyer to lawyer, but the general idea is the same. Preliminary deposition questions should be viewed from the point of view of the lawyer trying to impeach the witness at a later date.
UPDATE: David Swanner at the South Carolina Trial Law Blog has some other tips along these lines.