Wow, great advice, but some pretty....
First off, if it's a local beer can race, relax, it isn't the America's Cup. Second, your main goal for a first race is to stay out of the way if you are not assigned to job. If you do that well, you'll have done well. If you are given a job, ask what the job entails and who you take orders from. On some boats the skipper gives the orders on other boats, another person oversees the activities and the skipper just drives. Be very clear on who directs you and don't listen to anyone except that person during the activity.
If you can practice the job before hand on the way to the start, do it. Do not focus on anything else except your activity when you are doing it. If your are in charge of trimming the mainsail, do not get concerned about what is going on with other sails unless they affect you. There are other folks that are tasked with those activities, let them figure it out.
If you are just "railmeat", move when told and keep quiet during the sail. If you are on the rail pay attention to the other locations of other boats, wind shifts, etc. Lot's of commands are being given throughout the race and general banter is not advised. Socializing is for after the race. That being said, low voice talking with your railmeat neighbor is ok as long as it does not affect your main function on the boat.
As others have said, yelling or loud speaking will occur. That's okay as long as it is not derogatory. When it becomes personal, think about getting onto another boat next time. You should not tolerate that type of abuse. Captains or crew that verbal abuse their crew are a$$holes IMO and lack both people and sailing skills. I have been on boats that have this type of personality and it just plain stinks. Sailing is supposed to be fun even racing.
I you haven't already raced on this boat, fire an email to the Captain, introduce yourself, tell them about your sailing "resume" and ask what to bring. Bring what you need and not anything more.
When the race is over, help getting the boat put back together. If you liked the experience, captain, crew, and boat, say so to the captain and ask if he/she will have you back. If you didn't and they ask, be upfront and honest and let them know why, even if you need to talk to them out of earshot of others. Folks do appreciate feedback good or bad. Don't be mean about it. For example if a crew member was all over you for making a mistake, say to the captain, "While I enjoyed the overall experience, person A was riding me pretty hard about X mistake. It was my first race and I'm still learning the in and outs. etc. I didn't really appreciate them continuing the badgering well after the incident" See what happens from there. The Cap'n may not have been aware of it and act upon it. Good crew is hard to find as are good boats.
One last piece of advice - Go with an open mind, willingness to listen and observe and work hard, and be enthusiastic.
If you liked my advice/response, give me some rep points. If you didn't......well what do you expect, it was free.