From an autistic person's perspective who generally enjoys parties: (autistic person with both extroversion and social anxiety) The main goal is to establish and strengthen social relationships. There are a few other goals and notes the support this goal, but if you do not wish to do this, then do not go to the party.

Secondary Goals:

• Survive. Typically, you don't want to come away from a party feeling like its damaged either your emotional state or relationships. If this means taking a noise break so you don't melt down in the middle of the party, so be it. Phrases like "I'm just taking a sound break, it feels kinda oppressive in there." if anyone questions it. This doesn't have to be music, it can be people's voices reflecting off walls as people try to talk over each other. If there's a drinking game and you're asking this question, try not to win or lose. Be in the middle.
• Vibe. At some stage or another, it entered into my head that reading other people's social needs and responding to them was somehow manipulative. Maybe it is or isn't, but try to pay attention to the energy of the room. If people are talking about a board game or their kids first day at school, don't drop your hot take about Palestine. There are definitely parties where that conversation is the go, though.
• Push medium and long term responsibilities from your mind. For the next few hours, you don't have taxes or homework unless someone wants to commiserate about them with you. Commit an amount of time afterwards to unwinding as well (or having a hangover). You and everyone else here is trying to use their leisure time.

After that, there's a bunch of party specific activities that serve these goals:

• Conversation: Obviously. Hypothetically, you might have a standard group of friends that you hang out with on discord and play video games with. While it's fine to chit chat with them, this is not super different to voice chat. Try to engage with a new person or two, move between groups. Typically, people will gravitate towards the more interesting, outgoing, and/or hotter people at the party. This is fine for you to do as well, but be aware of whether you're monopolising someone's time, or they clearly want to end the conversation. If you have a special interest, try to talk about something else unless people want to know about it.
• Drinking: This is a cultural thing, but drinking in moderation can lower social anxiety a bit. Depending on your experience with drinking by yourself, bring your own drinks. You don't want to get too drunk (risky, embarrassing), and you don't want to be in a corner sipping drinks all night (some of the night is fine). Be wary of anyone who wants to get you drunk (especially you specifically). Also, watch your drinks.
• Dancing: Not my wheelhouse, but in some cultures its extremely weird if you don't dance. I don't have any advice here.
• Others: Board games, bad movies, asshole playing guitar in the living room etc. These are all fine and normal, but remember they should be bouncing off points for chill conversation. Don't be too competitive or whatever.

Ideally, after a party, you'll have a few new people to talk to regularly, and may get invited back to future parties or other social functions (hiking, video game groups, a roleplaying game etc). Don't jump down anyone's throat after the party with conversation unless they were really really into you. They probably are not.