Top 10 Misconceptions that Role Players
have about Role Playing Games

1. The GM is not your enemy
It is the game master's job to weave a tale that entertains, and challenges the players. No GM worth a damn is out to screw over his players. Think about it - what possible joy could be gained from that? A good GM recognizes that the best reward is achieving victory over adversity. Your GM wants you to win; it's expected. But they can't make the game too easy, or it will cheapen the effect.

2. Player relations trump character relations
Or put more simply, don't be an ass to the people you're playing with. The people you play with are real, flesh-and-blood humans that have real feelings. Your character is a make-believe fantasy. It's sad that I have to say this, but I've seen far too many people put a greater value on "staying in character" than respecting their fellow gamers. Well, there are times when you should step out-of-character so as not to risk offense. Always be considerate of the people at the table.

3. You do NOT need a balanced party
I wish I had a nickel for every time I've heard someone say "if you're going to join the game, you need to play a priest or paladin because we need a healer". What complete and utter nonsense is that? If the game master is worth a damn, he'll custom-tailor the game to the party's strengths and weaknesses, meaning that the game will be just as challenging and enjoying regardless of how the party is assembled. All fighters? No problem- you're a military squad in the middle of a war. All rogues? No problem- you're all involved in the biggest jewl heist the world has seen (I wonder who's going to backstab whom next). All clerics? No problem- you're a holy order trying to do what you can against demonic forces that seem to have infiltrated and corrupted the church. Saying that you can't function without this or without that is a bit like saying "my GM is so stupid, he actually bought a module and ran it as written without tweaking it to suite the story" (I may include that on some "top 10 GM Misconceptions" list later).

4. There is no perfect gaming system
I tend to get really impatient with people who argue to no end about how a certain game system is better than another. The rules are really not as important as most seem to think- it's the people you play with that will determine if a given game is fun or not. Role Playing Games are a lot like movies - there are a lot of different genres and play-styles. Some people like hack-and-slash games with a lot of combat. Some people like mystery and intrigue. And each gamer is going to have his or her own level of realism that they consider appropriate. There is no universal game system that will ever satisfy everyone.
Now having said all that, I will grant you that a complicated rule set can be very frustrating to learn (and GM), while a simplistic rule set can really feel stagnant and limiting. But just becuase you don't like a particular rule system, it doesn't mean that others can't enjoy it.

5. It's OK to lose
It's just a game. The world really isn't going to end if your make-believe character fails at some task or dies ignomoniously. You win some, you lose some- get over it.
I probably should also mention that it's very important for one player not to hog the stage light. In a game where you have multiple players, each one needs to have their moment to shine. If you're not gracefully stepping out of the way to allow other people to enjoy their chance at success, the GM may take the decision out of your hands and forceably remove you from the situation. In some instances, the only way for certain players to be useful is for the other players to be beaten down. For example, a character dedicated to healing is at his best when the other characters are at their worst. In these situations, it's very important for the GM to make sure you fail, just to keep the game interesting for your fellow gamers. Be mindful of that and try to roll with the punches.

6. NPC's are people, too
No, I don't mean literally; of course they're not real. But for the game to be immersive at any level, they have to act like real people. This means that they essentially behave the same way as you or me - they will take action to get what they want or to avoid what they perceive as bad. It's really as simple as that. An NPC isn't about to just hand over an item or help you out on a quest unless they have something to gain. It also means that an NPC isn't just going to stand around waiting forever for an adventurer to return from some quest. They have their own wants and desires, their own fears and concerns, and their own lifes to live.

7. Standard social etiquette still applies
RPG's provide a structure for hanging around with your friends, but never forget that you're still essentially making a social call, especially if you're playing at someone's house. Don't arrive early. Call if you're going to be late. Don't make a mess. Don't eat all of your host's food. Don't invite yourself over, and NEVER bring a strange guest. Basically, all those little social rules of etiquette that apply when you pay someone a visit still apply when you're meeting up to play a game... at least, they do if you want to be invited back for the next session.

8. Never assume that you can have something just becuase it's written somewhere
In order to maintain a balanced game, the GM has the right to restrict access to magic items, prestige classes, special powers, information, or anything else. When the GM says you can't have something, let it go.

9. Never assume that you can't have something just becuase it's not written anywhere
Conversely, don't be afraid to ask the GM if you can have some power / ability / equipment that you've made up. He may say "no" if your idea is too far-fetched, breaks the game balance, or would allow you to completely bypass some challenge he plans to throw against you later on. Then again ,the answer could just be a "yes".

10. It's OK to challenge the GM in the middle of a game... once
Game Masters are people too, and they make mistakes just like anyone else. If your GM doesn't seem to be implementing a rule as it is written in the book, it's perfectly fine to bring it up - he may simply have misunderstood the rule set. However, if the GM ignores your advice, then it's not ok to keep bringing it up during the game. The GM may be purposefully fudging the rules to obtain a certain cinematic effect. Or perhaps the rule is complicated enough that that it requires further explanation to understand. Either way, sit down and shut up. You'll have plenty of time to talk to the GM after the game, and see if you can come to an understanding.