If the party starts to get stale, or people seem nervous about moving to the next step even if you can tell they want to, just go grab yourself an empty bottle and get everyone in a circle. Tell them you're going to play a couple of classic games combined. What you do is you basically alternate rounds of Spin the Bottle and Truth or Dare.

Here's how it works:

Start with the person to your left, and place everyone with all the men together and all the women together. (This is important, and you'll see in a second) The person to your left starts and spins the bottle. That person has to kiss the person that the bottle points to. Here are the alternate rules that we use to even things out and make it more fair. If a guy spins a girl, he kisses the girl. If a girl spins a guy, she kisses the guy. If a girl spins a girl, she kisses the girl. If the guy spins a guy, he loses a turn. The bonus is, in exchange for having to lose a turn, is that if a guy spins between two girls, he gets to kiss both girls at the same time! (Just as a side note, we are in no way homophobic, but some swingers are, so we never bring up the situation of guys having to kiss at our parties. You can certainly modify the rules to fit your situation.)

Now, once the turn comes back around to you, you take your turn, then you announce that it's time for a round of Truth or Dare. We use the house rules that you can't take more than two truths in a row, and all dares must take place inside the house. Other than that, all bets are off, and we just work out way up to steamier dares as people get more and more comfortable.

Trust me, this works. We've had newbie couples over, and wound up having an awesome time. It works especially well if there happens to be more than one couple, and one or two non-swingers in the group who are curious, but won't admit it. Obviously play at your own risk, but I think if you give it a try, you'll find that you'll have a great time.