Before we go further, let me define roleplaying and rollplaying.
ROLEplaying is pure, unadulterated, communal story telling. It focuses on story-telling, character development, and the like. This is typical of many live chatrooms this author has been part of. No dice, no system, no real rules aside from the golden rule. It really requires a creative individual with a good command of the dominant language used.
ROLLplaying is primarily concerned with dice-rolling, system mechanics and the like. It is not mutually exclusive to roleplaying and, in this authors opinion, is dependent upon roleplaying when used in a text-based medium as often found online.
Now, the format that I'm talking about is called play-by-post. Some people call it RP chat (if the forum is a chat room such as Discord, AIM, ICQ, IRC, etc.). Some define Play-By-Post significantly different from RP chat. What I'm talking about is essentially RP chat within the mechanics of a particular system where the GM acts as moderator for the PCs, guides the story along, and plays all of the NPC roles necessary (unless some previous arrangement with the players was reached beforehand regarding one NPC or another). Essentially they are the moderators of the chat. The players tell their story and the GM makes sure everything goes along smoothly, describing new scenes/settings as necessary for the part(y/ies) involved. You can play this style in forums or traditional chatrooms or in more modern settings such as Discord or similar apps. Regardless of the medium used, the end result is communal story telling with some dice-rolling to determine outcomes.
With that in mind, over the years I have found that the best conventions to use in terms of structure of posts is those found in fictional novel writing. In essence everyone is gathering together to tell the story of their characters and how they interact with not only the world around them but with the other player characters as well. Once you strip away out of character comments, dice-rolling, and post editing (where possible) for clarity, what you have is a hopefully long-term community written story based around a group of characters.
If you're basically telling a story, then you would think it should read like a novel (even if not always grammatically correct or with perfect spelling), right? Well, what if it doesn't? What if people are just spamming out words as if they're doing an in-person group? At least in an in-person group (whether traditional 'pen-and-paper' or LARPing) you can use body language to know who is talking to who, the tone of voice can convey all sorts of things that you'd otherwise have to describe, etc. Basically you don't have to do a lot of scene or mood setting. Your actions/tone of voice set those for you. However, in a textual medium, it's impossible to know these things if you're not making them known, and it's even harder when you're not using some common punctuation marks to denote between speech, thought, and physical action.
If, as we've established, we're doing communal story-telling then shouldn't we use the same conventions that conventional stories use, such as descriptive text and all the punctuation marks that go with it?
Let me show you some of my conventions and examples after the cut.
The conventions I like to use when using a textual medium to roleplay are very similar to what you'd find in novels, and I typically RP in the third person (however one could just as easily use the first person pov, however just like in novel writing you want to be consistent so as to not confuse your fellow RPers).
First, when I talk, I try to be as specific as possible unless I'm addressing a group at large.
Take these two examples, the first is what I consider 'ideal' and the second, not (though more frequently encountered than not):
1): John looked out over the crowd, and upon spying his beloved Annabelle, started off after her. His love for her compelling him onward. Upon reaching her, he touched her shoulder and spun her around to face him, "Please don't go," he pleaded, "I don't want to lose you again!" The pleading look in his eyes matching the tone of his voice. He really didn't want to loser her a second time in as many years. The first time was hard enough.
2a): Please don't go I don't want to lose you again he told her once he caught up with her
2b): Please don't go
Now if there are only two people involved, it may be easy enough to tell who is being spoken to, though if you previously set the scene as happening in a crowded place, John could just as easily be talking to an NPC instead of 'her'. In the first example, however, the role-player not only specified whom they were speaking to, but also gave the reader a greater sense of urgency with regard to the plea and helped set the mood to which their partner could respond to in a more realistic manner. After all, if you're roleplaying as much as rollplaying, then such scene setting is of utmost importance. Only the player should know how their character would act in any given situation (which is reflected in the golden rule of roleplaying, never ever declare actions or words for someone else's active character (some common sense exceptions do exist, which is beyond the scope of this post)).
In the first example above, Annabelle has a wealth of information with which to work with so they can play out their character more in-depth. It's not meta-gaming to use things that you could normally be expected to pick up on in normal every-day conversation (tone of voice, body language, etc.) and what's more, the person roleplaying in response. Both formats of the second response, however, leave Annabelle's player in the dark as to not only who is being spoken to (especially example 2b), but the mood that is being set by John's player. It's even worse if their is a group of players and all of their characters are gathered in close proximity (generally within vocal range). Neither 2a or 2b identify who John's player is speaking to, but there is also no mood set and so the others have no 'body language/tone of voice' for which they can formulate a response. Sure they could guess, but John is going to be really annoyed if Annabelle's player winds up brushing him off because he doesn't sound earnest in the implied request or otherwise responds in a manner John's player didn't intend.
It's the same when doing combat scenes instead of purely emotive ones. Here are two more examples.
1a): Lt. Cmdr Henley picked up the phase rifle left behind by it's previous owner, and after checking to see if it could still fire, shouldered it and commanded the being she was chasing to stop or she would fire upon him.
1b): Lt. Cmdr Henley picked up the phase rifle left behind by it's previous owner, and after checking to see if it could still fire, shouldered it and yelled out, "Stop or I'll shoot!"
2a): I shoot at the monster. proceeds to roll to strike
2b) "Stop or I'll shoot!" proceeds to roll to strike
In either of the first examples, not only does everyone know that Lt. Cmdr Henley is performing the action, a ton of other visual information is provided, giving everyone a wealth of information that they can use in their responses. First we find out the character's name, which is useful when referring to the character without speaking their name (unless the opposing player would know the characters name). Such a response would be in the vein:
1) Robert heard the command from Lt. Cmdr Henley but ignores it, believing he's going to die regardless of what he does, while still running he calls out over his shoulder to her, "You'll never catch me!"
2) You'll never catch me he yells back at her while running.
In the first example you clearly see where speech and descpritions are denoted (the quote marks), making it easy for all involved to take in the information and process it. You also know exactly their mood (and you can decide what your character responds to and such).
Community-based, RP chatting/play-by-post requires that everyone contribute to the best of their ability. It allows for everyone to have a more immersive experience which, in this author's opinion, increases the amount of enjoyment everyone can explore. In the end, these are just suggestions or guidelines, however I provide them with the intent of increasing everyone's pleasure in playing at whatever kind of game you're engaging in, because if you're not having fun, then what's the point?