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. Or it might be that the top is subtly signalling 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. 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.