Your face is the first thing people notice about you when you go out into the world. Quite rightly, most of us put a lot of effort into making our faces look clean, healthy, and happy much of the time. Some people even go so far as to think of their faces as masks which they can use to alternately hide or reveal their true feelings to the world as each situation requires.
When you roleplay, your character is the mask you wear in a world where your real face doesn't matter at all - it defines who you are within this fantasy world and it determines how others will react to you as one of its denizens. Likewise, it deserves its proper amount of attention, like the care you give your outward appearance for your real life interactions. The method of caring for it is different of course, but the spirit and intention is the same.
Roleplayers have certain conventions you can use to quickly identify yourself as one interested in interacting with them. But more important than these is your attitude: just as the way you stand, smile, or keep yourself clean are all more important than the actual look of your face in real life; so, in roleplaying, a humble manner, a friendly approach, and a confident integrity are all essentials, whereas things like race, class, funny quirks and accents are all merely supporting elements.
A Persian man of wisdom was once asked: "Why do all the rivers of the earth flow into the ocean?" He answered: "because it sets itself lower than them all and so draws them to itself."
Humility, is, quite possibly, one of the most attractive qualities we can appreciate in other people, and it is the essential force that cleanses roleplaying activities of vanity, arrogance and Mary-Sueism. When roleplayers are humble, they read before they type, and pay special attention to the merits of other people's characters before trying to show off their own. Even if their character is evil and obnoxious, your humility in the way you play him will allow other roleplayers to find themselves strangely appreciating his otherwise unpleasant qualities.
Humility also means one takes some care to understand and respect the various ways people try to protect the special atmosphere people of a roleplaying server. In general, the rule of thumb is to stay entirely in-character in all /say channel chat and emotes, even when others around you are not. Whispers or other channels may be in or out of character, and you can always ask by phrasing your question in double parentheses ((like this)) - this designates that what you are saying is a temporarily out-of-character question or statement. Of course, on some servers, that atmosphere seems entirely broken already, so the mere act of respecting it in the way you speak and act can set you apart from others, and it often makes other people respect you.
"In the sweetness of friendship let there be laughter, and sharing of pleasures, for in the dew of little things the heart finds its morning and is refreshed." -- Kahlil Gibran, The Prophet
Friendliness shows itself in actions that reach out to other people and invite them to interact with you in some positive way. Among roleplayers, it is generally acceptable to introduce yourself and strike up a conversation. Some of my best roleplaying friends have been made in these spontaneous situations when one or the other of us felt outgoing, willing to take the risk of speaking first. Someone may not be available to talk at that moment of course, but likely your having started an in-character interaction with them will have brightened their day somewhat.
Shyness might be more acceptable in real life, when body language and other things can endear others to you. Wandering around without speaking a word in the game, however, will only make you seem like a mindless robot, since the level of human expression is so much more limited.
There are ways to invite other people to be friendly, however, which don't require you to speak to random strangers. Of particular note in this regard is an addon called Flag RSP, which allows you to write more details about your character's physical appearance and share these descriptions with others who use the addon. Although this is not required for roleplaying, it is widely considered the default standard for people to show that they are looking to roleplay with one another.
As you download this addon, however, note that Flag RSP is often misused, and its descriptions can often be poorly written. Don't be disappointed or overly frustrated when you see this, but exercise humility and patience in understanding that most people haven't learned the basics of how to write good physical descriptions. It's a topic that deserves its own article, and I plan to cover it soon. (Feel free to send me your suggestions about proper use of this addon.)
Another way to flag yourself as a roleplayer without using any addons is to have your character wear a separate set of clothing in non-combat situations. Usually people choose these items for their aesthetic appeal, but sometimes they can be particularly humorous, or, best of all, indicative of your character's quirks and personality.
Integrity has two meanings: The first is moral uprightness, but the second is a kind of completeness and consistency. Even an extremely wicked character can have this second sort of integrity, and indeed must have it in order to earn the respect of other roleplayers.
The most obvious element in upholding this integrity is to make sure your character's story and characteristics are in accordance with the previously established Warcraft lore. This takes some effort and research on your part, but really it only gets difficult or complicated if you want it to. Dramatis Personae provides you with a basic template for each race that you can modify a little bit to suit your own character idea. Although complicated backstories can be fun to create, don't expect them to necessarily impress anyone. When you're actually out there roleplaying in the game (or even talking with someone in real life, for that matter), you usually don't get long periods of time in which to expound on your life story.
This brings us to the more essential form of integrity, which is to make sure your characters story and characteristics are in accordance with the way real people think, feel, and act. Mary-Sues are notorious for lacking this sort of integrity. One principle that helps a lot is to think of your character's story less as a single, cohesive narrative, and more of a collection of scenes and experiences which influence who he or she is, punctuated by all the important events of recent Warcraft history. Often times the simplest stories can have the most impact, when they're detailed in a real human sense people can relate to.