So, you've heard that Local Super-Awesome Game Studio is going to have a playtest session in their offices, and that sounds like the most amazing thing since cats and captions came together.
Time to sign up and charge forth, displaying your prowess and knowledge, right?
Not so much.
It's like playing an RPG:
There are things you can do right, giving you a better chance to return for later sessions.
There are things you can do very, very wrong, ensuring you never come back. Hopefully no restraining orders will be involved.
This is the most important thing you can do as part of the entire process. They may call you to get more information about you, your background, advise you of what will be required of you to participate, etc. Odds are the person calling you is the one who will be herding you and the other guests around the offices during the playtest. You want this person to like you. Treat him or her with respect. Assuming that because it's a woman, she's a secretary (yes, I've heard this before) may be the last mistake you make in the process.
Remember why you're there
It is incredibly common for people to assume that this is their Big Chance to make an impression on someone in the game industry. If you try this, the best outcome you can hope for is a person who walks away thinking you're an overly-excited fan. More common: Once they leave the room, they send an email to the playtest coordinator requesting you never return to the building. There is a time and a place for everything, and you are there to get a sneak peak at something new and cool, and provide the developer with useful feedback to make the game even better.
Be respectful to others
You're in the building. You haven't accosted a developer, and you're actually in the playtest room. Everyone has opinions. Yep, there are a few key phrases describing this phenomenon that I'll pass on for the sake of decency. You may not like what others have to say. Odds are, this is true. Partially, it's because people are generally excited about being able to get into a playtest and say things before their brain has time to realize it was really dumb. Shrug it off. There's no need to call a person out for that. If they continue on, it's the responsibility of the playtest coordinator to perform riot control duties. It's your job to let them do so.
Remember, even positive feedback for another person can have negative effects: Don't interrupt others while talking, even if you agree with them and want to reinforce it.
Playtesting is not a gateway to making games
Don't get me wrong, if you pay attention to what the coordinator or any visiting developers say, you may learn things that will help you get in. This goes back to point 1, Listen.
Yes, you will get to meet some people who could help you down that path, but see Point 2. If you do a good job and they ask you back repeatedly, you'll do more to impress them by being a helpful, respectful person than anything you could say to them directly 99 times out of 100. If you decide to apply for a job at Local Super-Awesome Game Studio, put it on your cover letter that you participated in playtest sessions and leave it at that. Positive words from the playtest coordinator will carry a lot of weight.
Have fun (or at least try to)
News flash: You're playing a game before it's released. That means it's not done yet. While this may seem like common sense, you'd be surprised at the number of people who think that if the game is playable, it is ready to ship, except for a few bugs. This is very unlikely.
Testers spend 99% of their time testing a broken game, not one that is fun to play.
When you go in, expect to see bugs, crashes, and other annoyances that interfere with the "fun" aspect of the exercise. Don't complain. This doesn't help anyone. Trust me; the playtest coordinator is more frustrated than you are, because it is costing them valuable time (yours!)
Keep calm and carry on
It's really easy to get excited during a playtest, either positively or negatively. Add in multiplayer, and both passions and tempers are likely to flare. Get a dev in the room who asks for feedback, and it's easy for people to get excited about sharing ideas. The more relaxed the group, the more likely that suggestions will be asked for and listened to.
Just remember these guidelines and everyone will have a better, more productive time.
All that sound good? Check out some of these playtest info pages: