How do you keep a character from just devolving into yourself?

[Ionathus]

I think one way (though definitely not the only way or even a useful way in all cases) of avoiding it or at least keeping tabs on when it happens is to play a character that's fundamentally different from yourself.

For example, I'm a sarcastic pragmatist in real life, so if I play a character who shares those qualities, even if they are otherwise quite different from myself, it's easier for my own personality to blend into the character's without me even noticing. But if I play, say, an earnest idealist, most of their reactions are likely to be so different from my own that I won't just default to my own reactions (or if I do, it will probably be very obvious).

This is my go-to approach. After all, lots of people (myself included) choose roleplaying games for the chance to play a different character than themselves. So I lean into it.

I simplify it even further: I pick a single, core character trait, ideal, or rule that is wildly different from my own personality. I build off that base, and might introduce other character traits, but I keep that first one as the core of the character so that I can do an extremely simple check in my head: "does the action I'm about to take or the sentence I'm about to say conflict with this core trait?"

For example: I wanted my most recent character to be a real turd. Just very rude and selfish and not friendly at all (even if she had strong incentives to stick with the party and not go full Murder Hobo). My real-world upbringing was in a very polite society that requires the cadence of "please" and "thank you" and long, meandering chains of social cues and niceties, so I thought breaking from that ingrained behavior would pull me out of my comfort zone.

So I decided my core roleplay rule was "Vizka doesn't say 'thank you'." And it worked like an absolute charm. Whenever I caught myself about to say thank you, or please, or apologize for interrupting, I had to stop and think about truly living in a different headspace of how somebody who didn't "play the game" of politeness would get through this interaction. It was loads of fun and it got me really invested in her character. And it made the first time she bonded with the party and said a genuine "thank you" all the more meaningful for me.

[MoiMagnus]

Something I find important is to realise that there are two main components in roleplaying a character:

(1) The "talking" or "personality", which is what most peoples focus on in this thread.

(2) The "decision-making" or "values", which is something that is easy to forget.

You don't need (and probably shouldn't) detail loudly all the political opinions of your character. But having a clear idea of their values help maintaining consistency.

Because if you only have a "fake personality" that you put like a mask, each time you need to make an important decision, you'll instinctively call back the "real you" to make it, and this will erode your facade.

And those values don't even need to be that different from yours. If you don't feel comfortable with playing someone with different values, you can just take your own but change the priority between them.

[Easy e]

Values is a good call out.

I think some of my Character Arc and Rooting Interest are intended to get down to this.

One thing I really like about the Modiphius 2d20 system that I have seen/used is that a character's values are part of the number-crunching process and built into the system. You have a prioritization number in your attributes and values. For Tests, the GM gives the attribute and the player which Value it relates to the character, with the two together becoming a target number.

Pretty nifty way to prioritize some themes in the game and give players a good idea of the character from the mechanics.