How do I roleplay? Let me count the ways...
Whereas previously you were adapting basic things about your character, filling in blanks in his or her personality, backstory, and so on, now you start really exploring the details that make him or her special for you. Only after interacting with people that you have come to appreciate can your character really take on the feeling of an interesting person whose story you enjoy, like a longtime friend in itself, who has shared a lot of interesting experiences with you.
Most people roleplay with friends through a series of natural twists and turns that would come up in any intelligent being's life. These stories tend to be something like you might expect if you could see a TV show called "Personal Lives of Azeroth's Heroes," in that the stories you play out while roleplaying are less focused on the actual heroic exploits themselves, and instead deal with the relationships, feelings, attitudes, philosophies and all the other aspects of life that our characters would have, with the heroic, monster-fighting elements squarely in the background. The actual course of events is entirely unpredictable and can either be wonderful or boring, depending on the matching of your characters. They might be as simple as getting together and having a social party, or they may be as complicated as helping one another deal with serious problems that affect the way you each understand the purpose of your lives.
A common theme is romance. This is something some roleplayers will find enjoyable, while others will cringe in horror at the very thought of it. In fact, one of the harshest criticisms that old and burnt out roleplayers complain of is that roleplaying devolves into some sort of romance all too often. It may be interesting the first time, or even second time, but after some time it gets boring.
I confess, although I'm not at all burnt out on roleplaying, I no longer have any interest in getting my characters into any romantic entanglements. Some time ago, it felt interesting to see my character go through the ups and downs of a relationship in a way I never had in real life. I would even say that such roleplaying helped me to a certain degree later on when I got married, because it helped me understand that even though someone's attitudes and life experiences may be very different from my own, I can still put myself in their shoes and understand it. But now, I have plenty enough of romance in my real life that playing around with it in a roleplaying seems less interesting, and in any case I'm ready to move on and explore all sorts of other stories.
Some people like to put together more complicated storylines involving some degree of plot-driven adventure. One of the characters may be possessed by a demon, have some important items mysteriously stolen, or even get mixed up with an engineering experiment and accidentally summon their evil twin from a parallel dimension. All these things do have some basis in Warcaft lore, but to the general roleplaying public, they may seem cliche, unbelievable, and worst of all, Mary-Sueish!
However, in a small group of close friends, you may find that people are eager for some actual plot, and so they are open-minded enough to try it and see if they can possibly find something new in such a story. Even if the story doesn't exactly turn out to be a marvelous gem of English literature, it may still serve to let everyone involved have a good time. All this is great if that's the type of story you and your friends want to tell, but it's important to remember that people around you are not necessarily going to understand. They may assume you are just a bunch Mary Sues telling immature stories together.
One time after I just recently joined a new roleplaying guild, I was roleplaying with one of the senior guildmates for a while when another guildmate logged on and came to join us. The two of them immediately started talking with one another as if they had known each other for a long time, and their conversation gradually turned towards their ancient history together. It turned out that one of them was secretly a dragon in disguise as a blood elf but for some reason had been greatly reduced in his powers and could not return to his dragon form. Of course, my Mary Sue Alarm started ringing bells, but then I thought about it and I told myself: I'm new to this group – they already trust each other, and this is the story they want to tell. Who am I to decide that it's not okay for him to be a dragon in secret? To me the key here is "secret" – it's better in such situations to keep such things between close friends in the Core layer of roleplaying social interaction, because people on the outside (like me in this situation) can easily have trouble understanding it in the same way the close friends do.
In short, with a group of trusted friends you have the most possibilities and opportunities for roleplaying, but you also have to be careful not to overstep the bounds of what your friends are comfortable with, as well as what other people who are not yet really part your inner circle. If you really trust someone, you can even get into organizing events with them, perhaps even a wedding if you like them that much!