As someone who was old enough to remember sex before AIDS and Herpes Simplex XVIII, orgies were a regular staple of my sexual diet. I've even thrown a few, back when I was living in a pre-war Manhattan apartment on the Upper East Side from 1964 to 1980.
There are two sorts of orgies, the kind where couples gather to couple with other couples, and free-for-alls. The latter is sometimes problematic, what with finding the right ratio of yoni to lingam. Fortunately, some women can be especially accomodating, so it all works out in the end.
So, guest list is key. I was dabbling as an art dealer at the time, so I rubbed elbows with the downtown crowd. Just as variety is the spice of life, so it is the lifeblood of an orgy. Having just heterosexual couples at an orgy is so vanilla. No, it's a mayonnaise on white bread sandwich. I knew a number of gay couples, lesbians, drag queens, transsexuals, and most were welcome to attend. I say most because some of my lesbian friends were rather militant (this was the Seventies, after all), and loved to single out so-called happily married women as an act of subversion against the Empire of the Phallus.
Hosting an orgy is like hosting any party, except with ample fresh towels, lubricants, and nowadays bowls of condoms every six square feet. The liquor should flow freely, the food should not be especially gas-producing (save the Three Bean Salad for the church picnic), and the music should be cosmopolitan, exotic, and daring. Set a mood with music and lighting, something that encourages people to shed their everyday skins. Babtunde Olatunji's Drums of Passion always worked for me.
There's no orgy without some sort of scene. A wife gets talked into attending and then resents having to participate. A husband seems amenable to the idea until he sees his wife blowing a strange man. Some bi-curious straight guy gets buyer's remorse after sucking a drag queen's cock. Someone drinks too much, smokes too much. Words are exchanged, fists are cocked, cocks are fisted.
If this happens, separate the aggrieved parties immediately. Set aside a room for the inebriated to recover their senses. Keep everything cool and under control. Nothing kills an orgy like a full on fistfight. Before you know it, everyone's looking for their clothes and you spend the rest of the night getting semen out of your shag carpets. Knowing a good, discreet cleaning service that works Sundays is a boon.
Basically, if you throw an orgy, don't expect to get tons of sex. You'll get a BJ, maybe some tail, but you'll be too busy playing host or hostess to enjoy the pleasures of the flesh.
One last thing: we experienced orgyists call it The Goat. There's always going to be one person whose sexual proclivities define the corner case. The apocryphal example is the guy who shows up at an orgy with a goat on a leash. The practical example is someone who exceeds his partner's unspoken limits, with things like pain, watersports, scat, or fisting, for example. That's the sort of person you show to the door, and who's blacklisted among the informal network of hosts. You can only hope that things don't get out of hand, that people don't get hurt, and that you're not digging feces out of a shag carpet on a Sunday morning. But expect the worst and hope for the best.
Like I said, AIDS and other STDs killed the orgy in its purest form. But so did Plato's Retreat and the gay bath houses. I've been to a couple over the last few decades, but it's just not the same as those golden Sexual Revolution years.
So, good luck with your orgy, and have fun.