I am actually, legitimately diagnosed autistic. I'm not good at conversation, because I put a lot of thought into every word I say, which causes me to miss my chance and end up saying nothing. In fact it took me over 10 minutes to type this post.
This gets harder when I have the additional step of "how would this other person who is not like me act?", and I'm not motivated to give my characters complex personalities anymore because I know I'll eventually slip back into playing as myself.
My last RP group broke up over it, but I don't want to quit roleplaying because I enjoy it so much. How do I get better?
Technically that's what I'm doing, unless you mean a dedicated practice exercise outside of game sessions.
Play online over IRC or some other text-based medium.
It's technically practice, but you will be getting better at roleplaying both by doing and by observing and copying the other players. Eventually you will be at a level where you can produce competent and eloquent blocks of roleplaying text, and then it's just a matter of speaking those out loud.
Source: I have a child development degree and used to work with autistic chucklefucks like yourself.
My suggestion would to build up your confidence in everyday social actions. The more comfortable you feel with yourself in general, the more comfortable you'll be role playing.
Find a good group that'll be patient with you. Maybe even others who are in similar situations as you are. Knowing that its just a game and there are little major consequences for mistakes, your objective should and always be to have fun.
Create a sturdy character with a few major bullet points of personality. Reference these points whenever you can. Perhaps try giving your character a few catch phrases tied to the bullet points. That way you'll have a rehearsed response that would fit with your character. Once you get comfortable you can connect dots and add more to your character.
Never feel that you are abnormal. Everyone roleplays differently, everyone gets something different from playing. The common denominator is that everyone wants to have fun. Get in a good group and you'll quickly get the hang of it.
>I am actually, legitimately diagnosed autistic.
No one cares.
>I'm not good at conversation
>Technically that's what I'm doing, unless you mean a dedicated practice exercise outside of game sessions.
Then keep doing it until you git gud.
Just because you have trouble with something doesn't mean there's an easy solution to your problem. You're going to have to keep roleplaying and doing the best you can. That means pushing yourself to converse with people more, despite the trouble you have. You're not guaranteed to get better, but the people who do get better that's how they do it. I suggest just accepting that you are going to make mistakes and look awkward often as a part of your journey and rather than let them keep you from continuing take pride in the fact that you can learn from your mistakes.
If you insist on playing in person, which you shouldn't do just like a wheelchairbound shouldn't try to play soccer, the best option?
Play a charisma 5 character with in-character brain damage.
One of the best characters I played was a very intelligent elf that was one of the few survivors of a divine plague that left most survivors with no memories or social function.
He was a lucky handful that got off "light".
No memories, had to relearn speaking, language, social cues, etc.. Never really understood people, but was smart enough to emulate them... or at least their surface behaviors. Spent 18 levels being led around by other people who promised purpose and insight. Never got it.
>Play online over IRC or some other text-based medium.
Oh, I forgot to mention, I only roleplay online.
Even through text I'm noticeably slower than the other players. Drives me nuts.
Fellow autistic here, though it sounds like yours is more severe then mine. From my experience, your best bet for a new character is this: make your character autistic. Seriously, it solves your main problem. You are trying to avoid your own flaws in a character, but when you can't naturally avoid them, your best bet is to instead embrace that issue, at least for one character, to get used to your new group.