I found this guide online. Hope this helps!
It may be clear that you have to play the more passive games far differently than the active ones. If the action must be originated by the players with the game acting mostly as a referee you likely have to spend much time with thinking up your character and make it fit in the game world.
Start with getting a feel for the game. These games are normally strongly themed and getting a feel for the way the theme is worked out helps you with getting started. Most games offer you the option of experiencing the game as a guest. Guests do not participate in the game but can walk around, see things and talk to other players for a while. This gives you the opportunity to find out first hand if you like the atmosphere. It also gives you the chance to read the most important help in getting started. The on-line help of the game. Typing help (and on mushes +help as well) will give you a lot of background information for getting started on that particular game. Use this as the other players will expect you to have read (and understood) things. If you did not bother to find out what information is freely available then why would they bother in telling you? If this help is unclear then you can still ask somebody to clarify things to you of course. But make sure you read every available help at least once until you feel you have a firm grasp what the game is about.
Give your character a history. After all she is not newly born in the game even if it is to you. Where did she come from? What events shaped her personality? And how does she react to the common situations she will be facing in the game? Obviously this requires a certain familiarity with the theme of the game.
Keep your character close to yourself, but not too close. If you are new to roleplaying you may find it difficult to adopt a wildly different personality. If you are shy then do not immediately make a character that is the exact opposite. As you are getting better at roleplaying you will be more confident to handle different personalities. Or races. Or anything else the game offers.
Do not make your character too powerfull. Or too weak.. Either choice is boring, the first because there is no challenge to a god-like creature. If your character can make his enemies disappear at the snap of his fingers you will find nobody is interesting to rp with you. Story development requires conflict, and around your character that will last very short.
Being too weak has similar disadvantages. If your character can not affect anything around her there is nothing much to do for her. She will be the victim to any possible conflict and rp will be equally short and uninteresting.
The best advice to give here is: be modest and be reasonable. Give your character some strengths. And give her some weaknesses as well. Both fitting with her history. This offers you situations your character can confidentially handle and situations she will need the help of others for.
Get familiar with your character. This may seem a little odd but take the time to do this. You will have to decide how your character is going to behave facing unpredictible situations. Often in split second decisions. If you can really feel into your character you do not have to worry about how to do this. It will come naturally to you.
Do not be too explicit at first. You do not tell the story of your life to the first stranger you meet do you? Further, if you do not tell too much about your character it allows you to change your character somewhat to make it fit in more in the game. Without having to explain that last week your character had a fear of height but not anymore because it was awfully inconvenient for a species that lived on the mountain tops. Nobody gets their character right the first time and you have to live with the consequences for a long time, unless you do not tell everybody right away.
Make your character social. This is obvious. The aim of the game is to interact with other players and play out the reactions of your characters to the events, making up the history as you do so. If your character is haunting the forest all day, or sits on a tree top contemplating the meaning of life, your roleplaying won't be much interesting. There is a subtler side to this as well. Loners, or anti-social characters, are extremely difficult to rp well and still have a fun time while doing it. This includes characters that distrust everybody, are foreigners, have severe disabilities (mental or physical) or are flat-out evil. Most games that allow you to choose evil races restrict this to experienced players only. With reason.
Do not assume power. This is partially an extension of the advise not to make overly powerful characters. But also keep in mind that most games have a ranking system in place even if the game does not deal with that. New players start at the very bottom of that ranking order and usually rise only when promoted by higher ranking players. Never automatically. So you can not create a character of a knight even if that is suitable to the game. Not even of a foreign order. The other players will consider this cheating and most likely will refuse your character. Play the game by the established rules.
Wait. But wait actively. This is the hardest thing to do, getting involved in the game itself. You are new to the game, and nobody knows you yet. There are all kinds of ongoing plots, relations and histories that you know nothing of. This is unfortunate and you can mot force your way into things. You have to wait patientely for the people to notice you and start interacting. If the game has a friendly atmosphere most likely somebody will page or tell you soon after you entered but at times it may take many days before somebody takes notice of you. There is little you can do to speed up things, but it usually helps a lot by being around the public gathering places. What this might be depends on the game and game theme. Good chance is that it is the place where you find the most people on-line. Ask somebody there privately if you can join and go there. Sitting in a spot waiting does you no good. You must actively seek out other players and try to make friends with them. Also, do not jump in immediately in any activity going on, but stay back a little until you figured out the roles and behaviour of the other characters present. Of course you are free to offer an occasional remark and do whatever is fitting for your character to do. Sooner or later people will include you in the conversation, and likely sooner if you are not overdoing your actions.
Finally. Ask questions. You are new to the game and people do not expect you to know everything yet. They won't mind if you make mistakes and in general will be happy to answer your questions if you ask them privately. Most games have a command page or tell for this and if you use that you won't disrupt roleplaying. But keep it moderate and polite. Other players generally do not mind answering a couple of question but are probably a bit annoyed if you prevent them from actually playing the game themselves. With a little thought and reading the help you can work out on your own how most things work. If you really are out of your depth ask other players for information.
Some things to keep in mind:
When you are playing a roleplaying game you do not play it alone.
There are few or many other players involved. Each of them has her own ideas of what should be going on next. And there is often little time to ask permission to bring in an unexpected twist to a plot. This is one of the biggest charms of roleplaying, that you are going to be surprised by the actions of other players and that you have to deal with them. However, because people differ it is inevitable that from time to time things do not work out the way you would have liked them to. Throwing a temper tantrum when this happens is not going to be of much use. Keep in mind that nobody owns a story or plot in a roleplaying game. There is no director, but often there is somebody who wants to use a particular plot to explore the character they are roleplaying. Putting a new twist in a plot is perfectly fine, but hijacking it is somewhat rude. Take the time to see if the plot is developing before doing something dramatic. And if you are uncertain: ask.
Some final words of advise I have heard many times on the various roleplaying games I have played:
You are dealing with other people: don't be a jerk because you can. Not even when your character would behave like a jerk. At least not without privately informing the other player what you are going to do, and offering them a way of backing out if they really do not want to be involved in that kind of plot. The fact that you are roleplaying an evil character does not give you the right to ruin somebody's day. And not to mention their character. Even if to you it is only a game this does not automatically imply that the same is true to other players.
Do not accept it when somebody else is being a jerk. You are playing the game to have a good time, not to allow somebody else to vent his frustrations. Or to placate somebody's ego. If somebody is behaving like a jerk do not simply accept it. Ask them in private why they are doing that. And if that does not help. Leave the game. For a while or for good. Moaning about he fact won't do you any good. Feeling miserable because somebody was being exceptionally rotten to you either. This last is easier said than done unfortunately.
The game will not be all sweetness and light. After all the driving force of most (hi)story is conflict so you can expect a fair amount of that in any game that is interesting to play. The important trick is to remember that there should be a certain amount of agreement on the direction of a plotline and everybody should have some room to escape the final consequence of a conflict gracefully.
