Far too often, I see people who don't really understand roleplay much at all, let alone on tumblr. Let me make you a quick little guide.
A lot of these are considered "basic" or a given to learn.
OOC: Out Of Character; anything that isn't directly related to the roleplay
IC: In Character; Actions taken or words said as your character
PTH/PTK: Permission to Harm/Kill
Metagaming: Using information recieved out of character to give your character more favorable chances in any given situation
Godmodding: Making your character so powerful that they can't be defeated, and/or taking control of other characters without consent
A fairly debated topic that definitely needs some clarification and separation, for everyone.
Literacy level: How well you can read/write and understand in the given language. I've excluded "fluent" because someone can be fluent and still illiterate.
Illiterate/beginner: Frequently makes mistakes in grammar, structure, and spelling. Limited vocabulary
Semi-literate: Still making mistakes, but it's less frequent, and with a growing vocab (around 6th grade level)
Literate: Few mistakes on any score, still expanding their repertoire. Most use 3rd POV at this point
Advanced: Almost no mistakes, very dynamic and poignant writing, may or may not pull out words you may never see again
Length/Style: The way you write and how long it is.
One-liners: No more than three sentences, usually, including dialogue
Paragraph+ : A few sentences (considered three at the lowest), maybe a bit of dialogue, but not much else
Multi-paragraph: Between one and five paragraphs, not including dialogue (if each dialogue is separated)
Advanced: Six or more paragraphs, typically at the start of the point where people think it's long
Novella+ : Eight or more paragraphs, usually has a lot going on, and is almost always seen as "dear god that's long"
Mirror: Matching lengths to your roleplay partner, very much so a "here for the vibes" sort of flow
Be kind/paradox of tolerance. I don't know why the idea of being kind has gone down the drain, but please, be kind to each other first. Unless someone is outright mean to you, try to avoid "drama". The block button is your friend, actually.
OOC and IC barrier. The things that happen inside of a roleplay are fictional, and do not translate to real life. Someone flirting with your character or trying to kill them doesn't mean that they feel that way about you.
Meta/Godmodding is so bad. Nobody is actually having fun here besides the person on the ego trip, and it's so rude. Don't do this.
All forms of consent at all times. For character relationships of all kinds, or for doing actions against someone else's character. Always leave an out, consent can always be revoked.
Ask before you jump! Lots of blogs are selective, or just don't want to roleplay without knowing what they're getting into, especially on established posts. Unless there is a post labled "Open Rp" in some shape or another you should definitely ask.
Pinned posts, please! A lot of roleplay blogs will have a pinned post on them. It contains important information, including character background, mun info, and more! Sort of depends on the mun as to how much is there, but at the very least, we're all looking for the mun age, age limits, and boundaries.
Boundaries! Everyone has them, including you. Try to respect everyone's boundaries. A blog has an age limit, or maybe a list of people who should avoid it? Unless you fall within that a-okay zone, leave them be!
Adult and minor interactions? Need to be kept SFW. Teenagers should not be doing romantic roleplays with adults, let alone anything further. Adults should not let that slide, and minors need to block adult blogs who try that.
Sadly, there are bad actors here, like anywhere. The best way to manage them is to know what to look for. Knowing the warning signs for grooming saves lives. Minors: if you believe you or someone you know is being groomed, block and report the offending account, then take it to a trusted adult. There is nothing wrong with you, nor is it your fault, for falling victim to this. Getting help is the most important thing, and there is no shame for this. I believe that this website is a good resource on where to start looking for the signs, but I encourage you to do more research and be as prepared as possible. Please, stay safe out there. Not all adults are bad, but it's never a bad thing to be wary.
You may also see a handful of blogs who are known widely, but not well. No names will be named here. Some are known for frequently harassing others, some for questionable ships, questionable past actions or whatever the case is. It's not a bad idea to ask around and see what's what about that.