When you are finished with a topic in a deposition, don't move on too quickly. It's a common error, as Brad Bradshaw explains in his article, "Safeguarding Against Deposition Omissions"--
Another common mistake is failing to exhaust the witness’s answers before moving on. Asking, “Who was there?” is only the first part of the question. Once the witness stops listing names your next question should be, “Was there anyone else?” Otherwise, you run the risk of leaving the deposition with incomplete information. If that missing information emerges at trial, the witness will be able to claim that you did not let him finish (and the transcript will appear to support the witness). Sometimes witnesses simply forget a portion of the truth. Other times the omission is more sinister. But regardless of whether the information was omitted intentionally or unintentionally, by asking, “What else?” or “Do you remember anything else?” you will get a more complete picture of the witness’s position and reduce the likelihood of surprises at trial.
This technique is commonly called "boxing the witness in." As Bradshaw notes, "Only after completely boxing the witness into his answer should you move on to the next topic."
Bradshaw's article contains other good tips too, for example, what to do when a witness includes the phrase "at this time" in the answer. Recommended.