@Ghoststrider298 hi there, so this is new for me so I’ll do my best.
First get an idea of what the other person wants to do for a RP. RPing is no fun unless both parties are enjoying it.
Second, read the rules that people put in their RP books. They have rules for a reason and also people tend to put questions or passwords in the rules as well.
Third RP in third person. This means when you are controlling a character write it like a character in a book your reading not like you are the character.
Finally try to make your responses to people at least two sentences that have some details describing the actions or feelings of your characters.
If you need any more advice I’d be happy to help.