It's what happens between the start and the finish of a deposition that really counts. Even so, since I've written about starting a deposition, it can't hurt to write about how to end one too.
If the deposition is being taken to preserve testimony for trial, then you should end the deposition like you end trial testimony: on a high note and with a flourish. This post, however, is designed mostly for those who are taking discovery depositions. The important thing to remember about a discovery deposition is that you shouldn't end it too quickly. Take a break to look over your notes. Have you covered everything you planned to cover? Have you followed up on any important answers?
Even veterans end their depositions by reviewing what has come before. Since it might be the only chance you have to question the witness before trial, don't allow yourself to feel rushed. Don't allow your opponent to rush you either. Remember that during depositions, opposing counsel should largely be ignored.
Procedurally, there is nothing magic that you need to do at the end of the deposition except to say, "I'm done for now." The other lawyers who are present then get to ask questions until everyone is finished; if another lawyer asks questions, you can follow up yourself.
At the very end of the deposition, the witness will have to be advised about the procedures for reading and signing the deposition or, in the alternative, "waiving signature." If the witness is represented, his own lawyer will advise about signature. If this task falls to you, say something like this--
The questions and answers today will be typed up by the court reporter into a deposition transcript. You have the right to read the deposition and review the answers. In the alternative, you can also rely on the accuracy of the court reporter to have taken down everything you said accurately, in which case you can waive the requirement of signature.
Whether you should insist in some cases that the witness read and sign is beyond the scope of this post, but an update might be coming soon, in which case I'll provide a link here.