It's about time this was made. Although proper roleplay cannot be enforced, that's no excuse not to have a guide that you should try to comply with.
Disclaimer: These are not rules. You do not /have/ to roleplay all the time. The state of roleplay is just rather low and everyone doesn't know how to roleplay so I'm putting forward guidelines for good roleplay.
Let's talk about the basic vocabulary.Metagaming: This is when you use information that your character wouldn't know. If you, for example, called rebeljustin "Rebel" in the chat, it would be a form of metagaming. If you called him "Justin" it would be alright because it's his roleplay name (Nickname=Roleplay Name). However, if you call him Justin and you haven't heard his name IRP, then you don't know it and it's also metagaming. Metagaming also includes knowing who a demigod's parent is without asking or finding out, and using nametags to locate a player through walls. It also includes using something you read in the chat, but were not close enough to the coversation to logically hear.
Powergaming: This is, in short, forcing an outcome in roleplay.
Examples of powergaming: *Stabs her in the arm* *Shoots Justin with a fireball* *Grabs him* *Traps them in a tree* etc. The correct way to go about these would be *Stabs the knife toward her arm* *Shoots a fireball toward Justin* *Attempts to grab at him* *Begins to grow a tree around them*. That way the other players have time to react. You also shouldn't kill another player without their consent, generally speaking. But there could be exceptions. Other uses of powergaming could be the opposite, such as dodging a bullet or catching an arrow. at least 90% of players shouldn't be able to dodge every attack either, you'll need to get hit every once in a while. Make sure you react accordingly. The last major point powergaming brings up is godmodding.
Godmodding: Having an overpowered character. You can only take as much of a beating as a normal human can (gods aside.) If you're shot in the heart, you're going to die. If your arm is wounded, you can't fight as well, etc. You also can't immediately come back from the dead unless someone else somehow revives you. Die when you should, realistically.
Other tips:
Use common sense and logic. You wouldn't "Die laughing" unless you died and made a new character. You wouldn't shout at someone 500 blocks away and let them hear you. You can't do anything that a normal human cannot (some godly powers aside.) You can't jump incredibly far (Unless you're a child of zeus or whatnot) and you can't swim thousands of laps. It simply cannot happen.
Acting is reacting. React how you would. If someone just swam a thousan laps and you act shocked, you'll boost the level of RP because they'll realize their mistake. If someone stabs you and you let it hit you, act wounded. If someone dies, you can cry and mourn, but don't just give up on them immediately and move on, or try to run straight to the underworld and save them.
Play your part. If you're a 9 year old girl you simply cannot fight as well as a 16 year old boy. If you're a 16 year old boy you can't fight as well as a god. Know your limits, don't act like a cartoon character. Yes, sometimes you could try to do amazing things but less than 10% of your roleplay should be doing anything Whats up?erhuman and impressive.
For all that is holy, do not use emoticons.
This is my personal biggest pet peeve. Say *smiles coyly* not
Say *eyes widen in shock* not o-o. Just think of the literary way to accomplish things, not the quick and silly one.
Humor is ok, but don't just be silly. If every now and then you crack a joke that's fine. Don't do absurd roleplays.
/me is roleplay. That's what it means. It's for roleplaying actions. Use it accordingly.
Everyone can't be the most special snowflake. Let other people have their moments and you can have yours when you earn it. Acting like a lonewolf world-conquering edgy coolguy isn't as cool as you think it is. It's cliche, unoriginal, and awful to be around.