Use of Language
Perhaps this is not the most interesting part, but it sure is important. In roleplaying there are a few rules you should never forget.
-Choose ONE perspective. Either first (I-form) or third (he/she-form). Don't switch.
-You are in another world. Try to translate whatever you say as much as possible in to normal terms for that world.
(-This also means that you should not speak Out Of Character (OOC). Usually there are other ways of telling people what you want to say.)
-Make clear to the reader what you say and what you do. Most people put their actions/descriptions between **'s and their words between ""'s
-Do not use slang or abbreviative language (unless it's part of your character's characteristics) and try to avoid multiple exclamation or questionmarks.
-In most roleplaying areas not everyone can read minds. So don't do things like *thinks that someone should shut the door*. It's plain silly. Use "I wonder why that door is still open" or, "is it just me or do I feel a draft" instead.
-Try, whatever language you speak, to be as perfect as possible where it comes to grammar. Most people will not comment on errors, no-one is perfect all the time, but it is annoying for the reader.
-Do not SHOUT WHEN YOU DO NOT NEED TO (It's rude...)