Follow the broad-specific-broad approach, which has a track record of success: "Tell me about that meeting on April 1"; "Who was there?" "Anything at all that you remember about that meeting that you haven't mentioned?" Make sure you set the stage for each event, leaving no ambiguity about who, what, when, and where: "Did you take the letter to the mailbox or did someone else?"
Alternate key questions with less important topics. The skillful attorney obtains important testimony before the witness realizes what has happened. During your preparation, you may have listed ideal testimony that you wish to elicit. Create alternative ways to ask the same question and ask the questions at different times. This serves two purposes:
1) anticipating the need to rephrase a question if needed, and
2) catching the deponent off guard and eliciting a response that differs from one made previously.