Rule #1: Be a fan. All roleplaying games are collaborative efforts that involve the creative works of friends or colleagues, and in order to play, you have to interact with things that other people create. Be a fan of what your peers create! Latch on to your favorite things about your fellow players and help them to develop those things! The game will be so much better when everyone is invested in what everyone else is creating. As an addendum to this rule, you should create things which others can be a fan of. Think about your character, your writing. What is there that others can latch on to?
Rule #2: Make hooks, take hooks: The game is not just about waiting for the GM to shove adventure into your face. It is also about responding to the things your fellow players and your GMs write or create. Most people do not include things that do not matter. Engage, even with small things! Even more important is creating hooks on your own which other players can take. No one cares about your character’s edgy backstory unless you give everyone an opportunity to listen to it.
Rule #3: It isn’t just about winning: It can be tempting to take the actions which you recognize from a meta-perspective to be the optimal actions. This has its place, and is an okay way for your character to behave! However, no interesting story has characters which always do the perfect thing. The goal should be to create something memorable, which you can look back on and laugh, and that will not happen if your characters always do everything perfectly, always succeed at everything, and never take any risks.
Rule #4: Say “yes, and”: I take this expectation from the rules of improv. When somebody says something (for example, ‘the goblin in my backstory is a wizard’) within the narrative, it doesn’t help anybody’s morale, or the story, to try and deny that (for example, by saying, ‘that’s impossible! Goblins are never wizards!’) (unless it literally factually did not happen, of course). Instead, try and use what the other person created and expand upon it. It can create a much more interesting situation that way. Why is this particular goblin a wizard? Goblin wizards are vanishingly rare, there must be an interesting reason!
Rule #5: Express yourself: As GM/storyteller, it is very easy for my ideas to take center stage. However, I am a very player-based GM. The world gains complexity, depth, and humanity when it is created by everyone at once. However, that won’t happen unless the players express their desires! If you have something that you want your character to accomplish, say that, both in-character and out-of-character! Just because it isn’t part of the plan to start with doesn’t mean it can’t be part of the plan going forward. Furthermore, interact with the goals and aspirations of the other characters! The other characters are your character’s friends and peers, and friends support one another.
Rule #6: Give meaning to your choices; make choices that have meaning: Your choices, both mechanically and narratively, should have emotional meaning to your characters. Maybe your character is a wizard. Why? There must be just as much drama and emotion behind that choice as behind a person’s choice of career in the real world. They have mentors who supported them, rivals who challenged them, magic that they couldn’t master, a school they attended and emotions about that school. Even mundane mechanical choices like Power Attack and Spell Focus can have meaning if you give it to them. Narrative choices can add to your character. Everything from “what campaign are they in and why?” (for example, in a campaign against drow, perhaps your character’s family was killed by drow, or perhaps they are a scholar of shadow magic seeking to learn from the world’s best experts) to “how does your character refer to other characters?” (perhaps your character is irreverent and never uses titles, or perhaps they are exceedingly polite and never use nicknames). The point is, think about your character’s actions from their point of view, and decide the meaning, the reason, behind those actions.