In swinging, cleanliness is next to godliness. Being clean and neatly attired is always a good way to make a first impression.
Be polite and engaging and if you are new most couples are very willing to talk to you about their first experience in the lifestyle.
It would probably be a good idea for you and your partner to stick close to each other, unless you agreed before hand to mingle and meet more people. Much of this is just common courtesy and in some ways no different than the way you would behave at the office.
If you are invited to a house party the hosts will probably inform you of the “house rules” and you will be expected to abide by them. My rule of thumb is to act the way I would expect others to act if they were in my home.
If you are invited and reserve a place at the party and find that something comes up to make attendance impossible inform you hosts, they may be able to extend an invitation to another couple if they so wish. The same applies to the invite as well. If someone is considerate enough to invite you, it is equally considerate of you to respond to the invitation, not assume that the host knew you were coming.
Plan accordingly for the function you will be attending as well. If it is couple meeting couple, you may want to consider bringing yourself a towel for clean up or just to dry of if there is a hot tub or Jacuzzi involved. The same applies if it is a big swing party, you’ll want to be able to clean up afterwards. Keep your belongings clearly marked and you’ll never have to worry about someone accidentally using your things or vice versa.
Always ask your host if there is anything you can contribute to the party, food, beverages, condoms, and things like that. It is always appreciated and there will always be a use for it.
The bottom line is that good manners are always appreciated.