Be quiet while scenes are going on, or go to another room to chat!  The admiring or joking comment you think you are quietly whispering to the person sitting next to you is often heard by the bottom or top, whose senses are sometimes hyper-tuned and on edge. Would you want someone to whisper something about you right before you reach that point?  Be polite, and don't talk or whisper. Yours could be the remark that ruins a wonderful scene for someone.

Novices attempting to start conversations with the top or the bottom during scenes are one of the most common and astonishing etiquette errors at playparties with newbies in attendance.  Do not address comments or questions to the top or the bottom while they are playing!  Similarly, do not try to start a conversation with the partners while they are cuddling together after a scene.  What looks to you like a lull in the action while the top steps away to get a new toy or while the partners are whispering intimately together after a scene is not the moment to walk over and offer your comments! The partners are very focused on each other and on the intimacy of whatever they are doing together, and they want to maintain that focus even during short breaks. If you feel an uncontrollable urge to ask how the top ever learned to wield a knife so steadily, or to ask if the bottom isn't scared of having a nipple cut off, then go get a soda and ask someone in the social space.

Do not ever touch or get too close to the bottom during---or after---a scene. Bottoms are dependent on their tops: the bottom's physical and emotional well-being are the top's responsibility during and after scenes. After a scene, give the players a quiet space if they want to cuddle together. The closeness and aftercare following scenes and the bottom's emotional fragility usually last longer than it looks to outsiders. Give people time to come down. If you need to ask a quiet question, like "Would you like this blanket that's here behind me?" address the top, not the bottom, and be as unobtrusive, succinct, and quiet as possible.

Do not join in scenes, even if it looks like they are free-for-alls. A scene that might look to you like lots of folks are joining in to pleasure or otherwise play with the bottom might in fact be pre-arranged between the top and other acceptable players to look casual. Or it might be that the top is subtly signaling audience members he knows to be acceptable. Join in only if the top clearly beckons you in. If in doubt, check with the top.

Most people like to be complimented on their scenes. If you like a particular top or bottom, telling them what you liked about their scene is usually well received. But wait until they are walking about and socializing again! Asking interesting how-to questions is also a good way to make friends.

Do not intervene in scenes. If you are bothered by something you see because it seems extreme, risky, or even impossible to be consensual to you, find a host or DM to check on the scene, explain it to you, or reassure you. If a corrective action like a safety improvement needs to be taken, the host or DM will take care of conveying that to the top in an appropriate manner. When you are more experienced you will be able to recognize if something is possibly nonconsensual or unduly dangerous. At your first few play parties, plan to absorb and watch and learn. If something is too extreme for you to enjoy watching, then simply leave the room quietly.

Do not touch people's toys, floggers, etc. that are lying around without finding the owner and asking. Even if someone lets you hold a flogger, it is also courteous to ask again before swinging it through the air at an imaginary target or your forearm. Do not run a knife or wartenburg pinwheel along your skin to test its sharpness---the owner might have gone to pains to sterilize the blade in expectation of an upcoming scene, and sharp edges break skin without always leaving marks or drawing blood.

Clean up play furniture or play areas when you are done using them. Pick up your toys so someone else can use the play area without stumbling on your belongings. Wipe down the play furniture so it is not sweaty for the next person, and if any bodily fluids were spilled accidentally, clean them up thoroughly---hosts often provide appropriate cleaning materials if you don't have them on hand.

Do not hog play furniture for hours on end with your own scene. If play furniture and play spaces are scarce, ask the host for an estimate of a reasonable amount of time to use it.

Be tolerant of things you didn't expect. In particular, even if you are fascinated, try not to gawk noticeably at something you personally have never encountered before. Watching and learning are fine---and are often exactly the point, but there is a social norm in each group about what is appropriate astonishment to show to those around you. If you have never seen two males play sexually and lovingly together before, or if you find watching the two women playing together across the room really hot for you as a voyeur, or if you have never talked to a cross-dresser close enough to actually hold a social conversation while you are standing around getting soda, get a grip on yourself before you start behaving like a ten-year-old telling a joke with a naughty word in it! If you never expected and are shocked by the amount of blood flow from a ritual cutting, or by what appears to you to be the hate-filled screaming and cursing of a bottom raging at her top at the height of a difficult scene, or if you never envisioned seeing a piercing of a needle right through someone's nipple, or if whatever else you didn't expect and are suddenly encountering seems extreme to you, then the astonishment is probably yours.

In advance of the party, read a few books on BDSM and try to pick up a few pointers about what you might see. You might even pick up some fine points of etiquette, like how to behave toward a slave in the presence of the master. Like: never treat a slave as if he/she is a slave to you!

You can and should talk to the host and/or DM during the party or, if more appropriate, afterward to ask unanswered questions, say thank you, and follow up in any ways you like. If you felt uncomfortable about anything at all at the party, talking to the host or DM afterward is an excellent idea! DMs usually very much want to help their guests learn and sort themselves out according to comfort levels. They also desperately want feedback so they can create environments that accommodate a variety of comfort levels and so they can decide what kinds of play and which attendees make for enjoyable parties. If a DM never hears about the individual that harassed you or that you felt some kind of play you watched was unnecessarily dangerous and you had no DM you could approach and didn't know the customs about how to handle the situation, the host cannot possibly make the necessary reforms. The host wants to know, and it is your responsibility as a responsible attendee to take the initiative to inform the host.