How is this a problem?
At face value, playing with the people you know well would seem like the opposite of a problem. After all, you already know one another, so the usual sorts of drama that apply to interactions are eliminated or at least diminished.
Unfortunately, that's replaced by a different problem, one that can be illustrated with a simple question: Can you remember the name of a single character Tom Cruise has played in the last eight years? Can you do so if you aren't allowed to fall back on Mission: Impossible?
It's nothing to be ashamed of. The man has a distinct face and voice, and he's long been bankable enough that he's essentially just Tom Cruise in everything. It's a waste of a guy whose only real talent is acting, but it demonstrates the problem when people know who you are. You aren't seen as an actor any longer; you're a well-known personality stepping into a role with everyone sort of winking and nodding at the idea of pretending you're someone else.
In fact, as a result of this, not only do misunderstandings not decrease, they increase. People will sometimes think of your character as a de facto mouthpiece because they know who's behind the scenes, and that means that your character's actions are sometimes seen as being your own even when nothing could be further from the truth. Does your character have a crush on someone? You must have a crush on that character's player. Do you hate someone in the game? You probably hate the player in real life.
And sometimes your character won't be taken seriously, which is even more fun than getting into arguments about why you dislike people you don't dislike in the first place, let me tell you.
So what can be done about this? To a certain extent, there's nothing you can do. If you're good enough as a roleplayer, you can both put your own knowledge of another person aside and play a convincing enough character that it's easy to think of the two as disconnected entities. But there are a couple of tricks you can use to at least help the process along slightly.
Play against type
One of my most frequently recurring characters changes from game to game but always has certain core traits: She's gregarious, polite even to close friends, fashionable, given to flights of fancy and random whims. And one of the reasons she crops up time and again is because several of these traits are more or less completely the opposite of who I am in real life.
I mentioned above that it's easy for people who know you well to misread your character actions as your own actions, and this is only exacerbated when the character bears some prominent similarities to you. It's a short skip from there to assuming that the character is in some way serving as a mouthpiece for the player. Yes, this is occasionally true, but that's bad practice and thus should not be indulged.
Having a character who's visibly different from you makes it easier to sell the idea that Sven and Paul are two distinct entities and that Paul just happens to be pulling Sven's strings. Besides, characters who are essentially the person you already are wind up coming across as kind of boring. You don't want to be boring, do you? Of course you don't.
Feel safe to indulge and plan
I've called Ms. Lady my favorite person to roleplay with in the past, and this is true for many reasons. If I had to pick just one, though, it's the fact that I can have one of my characters beat the snot out of one of her characters for several minutes at a stretch without any fear of drama or frustration or protestations of "no, you shouldn't be able to do that because of reasons." And the inverse is just as true.
Why, you ask? Because this is a woman whom I've been best friends with for over 12 years now. She knows me well enough to know that our characters' disagreement is not some sort of subtle dig; it's just a matter of our characters being at odds. So we can go to extremes and communicate on these matters from a neutral point of view, figuring out what would be the most dramatic possible interaction rather than just aiming for what won't rock the boat.
So we talk roleplaying. We plan. We have loose ideas for where we want our characters to go in the future. And the net result is that we treat these characters as external entities, people whose interactions entertain us without being extensions of our personality.
If you know someone well, you don't have to section off your friendship and your shared enjoyment of roleplaying. You can make those work in concert, planning out what characters would do and taking things to a level that you otherwise wouldn't because you know the person on the other end will know when to stop or crumple or whatever. You can start a character romance knowing full well that it's not a stand-in for a real one, and you can end it without a sense of betrayal or cruelty. You can have one character plot against another when the characters are all in the dark but the players have full knowledge of what's around the bend.
It might lack some spontaneity, but it definitely goes a long way to making a friendship a benefit rather than a hindrance.
Feedback, as ever, can be mailed along to firstname.lastname@example.org or left in the comments below. Next week I'm going to finish -- or at least continue -- my little descent into madness. After that, I'm going to talk about the lies our characters tell themselves.
Every Friday, Eliot Lefebvre fills a column up with excellent advice on investing money, writing award-winning novels, and being elected to public office. Then he removes all of that, and you're left with Storyboard, which focuses on roleplaying in MMOs. It won't help you get elected, but it will help you pretend you did.