Entry 1. I'll be slowly adding points here to help with lore, world-building, and character construction. Pointing out what I and others have seen as the pitfalls of RP. The point isn't to bash on anyone writer and for every rule, there is an exception. This will be compiled by myself. The purpose is purely edification, debate is welcomed as long as it remains tasteful. This is an open discussion so other players can add their own thoughts on common pitfalls or errors that cripple narratives.
As a roleplayer and writer, I follow a simple rule, I ask myself a question, a basic question. "What do they eat?" If any fictional society is to remain mildly believable it is important to showcase how the basics function. While the reader doesn't need to know the housing market, things like food, water, basic work available, and their cultural way of life are vital points that must be addressed or hinted at. The next biggest hurdle is consistency. I can suspend my disbelief that Superman's eye lasers can hurt someone. But, if they suddenly cure cancer, I will feel betrayed or insulted as a reader. This is why large sections of the Star Wars community do not like the new trilogy. This also happened to GOT with the teleporting around and out of character/unearned actions.
Also, your characters must have faults. Both in terms of powers, but more importantly, personality. No one likes reading about or watching a character who is beyond broken with no inherent struggles to endure. It makes them unappealing and not marketable. Lastly, the hero's journey troupe is vital. The audience needs to see your character's progress. This is why making a new RP character who is already an anime protagonist at the final arc on day one will tarnish 98% of plots. If you can easily one-shot 99% of threats, there is no tension, no stakes, and your partner and readers will be bored.
One struggle I have run into is having characters that are 12-21 OOC years worth of RP, is keeping inherent flaws in their kits to avoid this trapping. So, for example, Somber is purely destructive, she lacks defensive means and has no great mobility that doesn't trap her in a straight line. Faaria is a powerful Djinn, however, she has little means to defend against physical, and her attacks are not all-encompassing (As in limited aoe size, and being thin like a card or a 6-inch beam in circumference). This is partly why I prefer OC's that are established, as they tend to be more likely to avoid these mistakes. While a freshly new (Made on the spot) character isn't inherently bound to these faults, it requires amazing writing to convince me that they have earned their position. And most people are not good writers, just like most people are not good runners. Fandom RP's are the worst in this regard, not because you can't have a compelling narrative and interesting characters with them.
But because more time than not if you're doing a Bleach RP, someone is playing a fantasized version of themselves wearing aspects of Ichigo, playing as their granddaughter with all of his powers earned near or at the end of the Magna/Anime.
In summary and quick additional points to be expanded soon in more detail.
1) What do they eat, drink how does the world function on a basic level, as well as, the law of magic or tech needs to be explained or hinted at.
2) Mary/gary sues kill plots. Unless the point of the plot is a reference to that cancerous troupe. And if your characters are physically/magically OP that is fine, give them a crippling personality fault to compensate.
3) Consistency, consistency, consistency with the rules of your character and world. Nothing annoys me more than someone who says their character is selfish, suddenly being altruistic because they don't want the ire of fellow players or risk conflict they may not be able to win.
4) Power scaling is vital. It is hard to balance a character, let alone one that has been through many, many arcs or battles. However, a good writer can and will maintain some level of clear weaknesses.
5) Don't play fantasized versions of yourself. This is a huge pitfall, you can clearly tell who does, because, if you have an issue with their character they will take it personally. Because you're not attacking Billy the vampire, you're attacking themselves. And no, this doesn't mean your character can't share a small number of similarities.
6) Roleplay. You are playing a role, don't make someone who can do everything. This includes combat to knowledge.
7) Misc. All my characters are vastly different, not just in how they fight, but in how they see the world and act. If your characters are all the same, that is a bad sign of your writing capability. IMO that either means you lack any creativity, or you're playing yourself, or you're playing the same character with a different name due to laziness.
This is merely my own opinion, based on about 20+ years of roleplaying across countless mediums. It is in no way law or fact. I felt I needed to add this here to help with the common pitfalls I see people plummeting into it. All these points will utterly shatter the suspension of disbelief, and by extension immersion. If you're offended by this, I'm sorry, but I have the right to lay forth an articulate opinion. Keep in mind that any of the styles I attacked, I did specify they can work, just rarely. If you're not part of the norm, and are that exception, no need to be hostile. I welcome open discourse, especially over PM to prevent the derailing of the thread. Thank you, and I hope you guys take something away from this. I will be expanding soon on much of these points and other issues as time goes on.