TL;DR: There is no time upon entering a party to assess all the people there, unless you're among the first 3 or 4 people to arrive. Use the occasional glance around the room to remain aware of your surroundings, but focus the deeper reading on the people that you're interacting with.
This upset them as I wasn't paying them enough attention during the conversation, and I believe their reaction was justified. I was also resorting to looking at one person after another, which in a large group will take a long time - much longer than most people take to 'read a room'.
Just like you, I've had social skills training, and just like yours, mine taught me to read the other person, but never reading an entire room. Here's what I've come to realise over the years though, based on that training:
When in a group, you lack the amount of time you have in a one-on-one conversation to keep judging the mood, reactions and engagement of a single person. Even in a one-on-one conversation this time is limited, in a group setting even more so. The bigger the group, the less attention you can give each individual, and the more you'll have to go on a sample of the reactions around you. Spending time looking at each individual closely will mean that you're distracted from the conversation at hand.
When entering a new room, full of people, there also isn't time to stand in the doorframe closely observing over a dozen people.
This website, written by someone that claims to have over 10 years of experience in training other people's social skills, states:
look at the setting, take some time to observe and make mental notes. Resist the temptation to jump into a conversation right away (or conversely run from the room in terror). On the other hand you don’t want to appear as a wallflower disinterested in connecting. Some questions to ask yourself include:
- What is going on around you non-verbally?
- What are people doing?
- What’s the mood?
- Are you entering a conversation that’s already been going on?
- What’s the topic of discussion?
- Who are the players?
And remember, you've only got a few moments to do that upon entering a room. Now, the best way to go by this information, as I've come to realise, is:
1.) A quick glance around the room to pick up the 'high level' non-verbal clues and a sense of what people are doing.
Usually, when entering a room, look around that room, take just a glance at everybody. Don't worry about it yet, just register where people are sitting and where the free seats are, how many people there are and what they're generally doing. Are they sitting and listening to someone, or telling a story to which multiple others are listening? Is everyone looking at you, standing in the entrnace? What sounds are coming from the room? Angry shouting is probably bad, laughter and smiling faces sounds good.
Usually, in The Netherlands, the first move you make at a birthday party is a meet and greet with the host. Take some time to shake their hand, congratulate them, present them with their gift and exchange some pleasantries. Try and read their mood, are they happy because the party is going well? Cast a glance around the room, and focus on your host again (maybe when they're unwrapping their present?). Repeat as needed (and as time allows) for a few times.
This site gives some nice pointers on what you could look for when entering a room, and what those non-verbal clues might mean, as well as some guidance on the best ways to engage the group. There's different ways for different readings of rooms, I'm going to continue with a happy, fun birthday party, such as described by the last point on that website.
Try to pick up what's going on around you non-verbally, in the most global sense.
2.) Focus on the conversation/discussion that is going on already, take a seat and take some time to understand what is being talked about, and how.
Focus on the people talking first, identify the players. Read their mood, their reactions and engagement in the conversation. The great thing about groups is that they probably won't be talking all at once. Sit down, listen, and observe the closest person to you that's talking, and then the ones that are responding. Observe on a person by person base, just like in a one-on-one conversation.
From what I've experienced at birthday parties, if there's more than a dozen people there's likely to be several subgroups having several conversations, try to just focus on one for the moment. If it helps, it may be easiest to pick the one subgroup that has that person you already know. This will free up some 'processing power', as you don't have to worry about reading everyone, but only a few people at a time. If two or three people are having a pleasant conversation, you know enough and it should help you feel comfortable enough to chime in.
Identify who's talking, what they're talking about and how they're talking about that, just like you would in a one-on-one conversation with a person
3.) Reading while participating in the group.
After having a gotten a quick impression of the room, it's time to participate. Otherwise, you'll end up as in your experiment: On the sidelines of the conversation, with people thinking you're not interested.
If there's not a lot of conversation going on, and you notice people seeing you when you walk in, a round of introductions to at least these people does work nicely. If people are so busy having their conversations that they don't really notice, pick up a chair, listen, and at an appropriate time cut in with a remark of your own (make sure that it is relevant to the conversation!). If you feel like playing it easy, pick the subgroup that holds your friends to start.
Group dynamics at a party are likely to shift. People will get drawn to your conversational topic, or drop out. Take a few pointers from that first website on what to pay attention for when reading while participating:
- Read others reception, are they interested in what you have to say?
- Gauge the length of your talking, conversation needs to be give-and-take.
Even once you're a part of the conversation, keep the deeper observations to a sample. It's not necessary to keep track of over a dozen people at a birthday party, focus on your seating neighbours/your side of the table. If they start acting and looking bored, concerned, agitated or worse, it may be time to either sit back and let the conversation continue like it did before you chimed in for a while, or let it move on/actively change it to another subject.
On the other hand, take an occasional glance around the room. It might attend you to stuff as 'speaking too loudly' if people all start to drop their conversations and start staring at you.
Take an occasional glance around to remain aware of your surroundings, but focus most of your reading on the people you're directly interacting with.