(There is a tinyurl link to this page, for ease of linking people: http://tinyurl.com/iirpguide )
The Island's roleplaying community is for the most part a remarkably warm, open group of individuals with lots of varied levels of experience and interests.
Some people are out for a lark and don't care too much about elaborate character backstory; they're interested in writing silly scenes to blow off steam or to put their character into situations they find interesting. Some people are serious writers (not too srs, though) who put a lot of time into constructing stories that hone their own writing chops and entertain other players. Other people fall in between these two poles, or shift back and forth. Whatever your interests are, you'll probably be able to find someone else who is on your wavelength.
For the most part, though, everyone most respects the people who take the time to read and/or think before they dive into the community.
Here are some tips if you're just getting started. This is not the gospel - - you can take this advice or leave it. You'll be just fine if you hop right into things and adapt on the go.
It's helpful if you come up with a personality and a background for your character before you start writing. How are they reacting to having been abruptly pulled away from their homes, or families, or friends? If someone they didn't know very well was being picked on in front of them in public, what would they do? What makes them nervous? What do they think they're good at? Are they actually good at it? What aren't they any good at? How will their personality change, if at all, if their race were to change on the Island? What kind of people do they admire?
Even if you never share any of this information in-character on the Island, other writers can often sense that you've thought about it. That's because the effect of having thought about these things is usually that you're able to write your character with a distinct and consistent personality. People will be eager to play with you as a result - - they'll want to get to know your character, 'cos you've got interesting things to say about your character and you can answer their questions. If the example questions above seem like they don't apply to what you want to write, ask yourself questions that you think are more appropriate.
Go to any area with a banter or story chat and scroll down to the bottom. Right underneath you'll see a 'Customize Character' link. If you click on it, you'll be able to input a 255 character biography. You can also make a much smaller, quickie bio for people to peek at when they mouseover your preview icon in any chatspace. That's still in Customize Character, but under the 'Physical Description' portion. There's a few other things you can update from this screen, as well.
People check biographies to get a rough idea of who they're looking at and how that person behaves. If someone mentions that their character has a weird and prominent scar, you can use it as a conversation point. If your own character is boisterous and a little bawdy, but really doesn't mean anything by it, you can write that into your bio so people don't worry if your character is smarmily hittin' on the dudes and ladies.
Find some people whose styles you like, some people you wouldn't mind being friends with. Check out what they're doing. Where do they hang out? What kind of stuff are they writing? Join their scenes, or if you're feeling shy, Distract one of them to ask if they would be keen on including you. (They will say yes. It's basically guaranteed.) As soon as you've met a few people in-character, you can join them in Outposts whenever they're around and they'll introduce you to everyone else.
Even if you haven't read tons and tons of scenes (or any at all), don't be afraid to launch into things if you're ready to rock and roll and you feel like you know what you're doing. People will be happy to meet you and, if you need help, to give you a hand. If you want specific advice or guidance, there's a list of volunteers on the advanced roleplaying tips page who are always happy to answer questions or join you in a scene.
Although there are lots of exceptions, most peoples' characters show up on the Island as humans, with human abilities. There are lots of characters with spooky-super-cool-oh-my-gosh powers on the Island, and you can write one too - - in some cases, right off the bat, but in most others, after you've stuck around for a little bit. As people get to know you and your character's story, they'll believe more of what you have to say. There's this thing called 'suspended disbelief' in writing where you can get your audience to accept whatever wacky premise you throw out there as long as you've established some (subjectively) logical reasons for it. You'll automatically earn that privilege over time. If you want it from the get-go, you'll have to carefully convince your audience that your character deserves whatever crazysexyhot abilities you're giving them.
Playing within the world's canon. Read the Museum text, the in-game stories like the Stranger and Watcher arcs. Figure out what you've got to work with and if it interests you, build on it. Situate your character within this world. You could play your DnD / WoW / anime-influenced / original fiction character here on the Island.. but you could play them just about anywhere. This is the only place you can play an Island character, and we've got a really interesting world to play with. If you've got favorite characters, consider making someone new for this setting.
This stuff should get you off the ground and well into the thick of things. For more tips and talk, check out the Advanced Roleplayer's Guide.