Nothing builds rapport faster than humor. It brings the selling process to a real level. It brings out the truth. I have found that many truths are revealed through humor. The earlier you get a prospect to laugh, the better.
Laughter is a form of approval.
Don't make jokes at someone else's expense. If the prospect knows the person or is related to the person at the brunt end of the joke, you're dead meat. If it is repeated, I guarantee it will be mistold or altered and will surely come back to haunt you. Use yourself as the example or victim of the joke. It shows you're human and can take it.