Evan Schaeffer has post entitled In Depositions, Beware the "Usual Stipulations" that links to Ernest Svenson's post on deposition tips for young lawyers. Both links have some great ideas for depositions. In fact, the only tip I'd add is that the two most important words, for me, in depositions, are "Anything else?"
Q. Can you tell me what happened on [the date of the incident]?
Witness. Well, it was dark out, and Ms. Doe came in to buy a soda from me, and we talked about her baby, and then it was pretty much quiet until the accident.
Q. Anything else?
Witness. Um, well... let's see. There was that fellow that came in just before the victim, but he didn't say much.
In other words, let the witness give you the information. Don't fight them by asking limited, yes-or-no questions unless you really need to do so.