The first rule is that , in general, much of the swinging encounter needs to be coordinated by the women. They will have feelings during the encounter , and it's better to let them set scene. If you, as a guy - want to scene, and she doesn't. Then don't. Consensuality is the basis of kink.
On the other hand, if she does want to scene - let her choose the playmate. A hidden rule that many guys won't read into the scene - is to keep your attention focussed on your current mate. In a threesome, it's easy to have one person stranded. Swingers like to do foursomes, where soft swaps are possible. This helps to even out the feelings / and have the emotions happen in a way that can be harmonized to activity. Passion can play strange tricks on people - a woman can want to scene, and then the minute her man penetrates the other woman, she might feel like she wants to cry. This is not something you need to do. She might, however, feel perfectly happy being more beautiful than the other girl. Threesomes are usually not always fair. Foursomes on the other hand - have a sense of fairness. A woman playing with another man, while a man plays with that man's woman - has a sense of bond between the two women. In order to make it work, the women need to initiate it and it should always be the woman's choice.
As a form of social movement, swinging became a kind of mass expression in the seventies - with places like Plato's retreat. However, into the eighties, and with a broad misunderstanding of HIV - the type and quality of interaction changed. Plato's retreat experienced a rapid decline through the mid eighties. Almost in answer, several other clubs sprung up in its place. The sixties and seventies were a time in which social expression reaced new heights. Women , in this lifestyle - are empowered. Women are not belittled - in contrast, a vibrant scene often centers around them.
That part of the sexual revolution became, for many, a lifestyle - and there really are several ways to approach it. Swing clubs can be a venue for people to have an encounter, in a safe manner. They can also be a place for exhibitionism and group encounters. Always, of course - knowing your boundaries.
Humanity started off as tribal - roaming from place to place in a group. Only later, when mankind switched to an agrarian culture, and the concept of land ownership was introduced - did we entertain the concept that a woman could be like a possession. Bound to home and land. In the dawn of man, it was common for women to share the responsibilities of raising children, and for men and women both to feel a close knit sense of attraction.
Humans are unique in that we find within us strong connection and the ability to mate with a partner for life. And the sense of that pairing often removes emotional chaos. Love, pleasure and duty are often intertwined.
However, swinging often relates more to open sexuality than polyamory - it is usually a practice by which a couple can explore their own sexuality together, and not necessarily engage other couples or partners. Done in a group environment - we acknowledge the connection all human beings share in a safe, sane and consensual way. Even if in ancient man, we found the roots of polyamory - we celebrate in our culture and society the benefits of single partners.
But perhaps, also - those who would choose to enjoy the company of congenial friends in an erotic setting - might act to relieve some of the unreality of our expectations, as couples, in married life.