When I was 18 I started volunteering, and on my first day there I decided I was going to force myself to be confident and outgoing and talkative, instead of the shy, timid kid I was at school. But I wished I had just been myself (still friendly but not afraid to non-verbally admit I was shy), because it just ended up with me making a fool of myself and them humiliating me about it (although them being cliquey didn't help). But I think by being something I wasn't, I was just annoying everyone. It just didn't work. I failed.
So now I just be myself more. If I have nothing to say then I say nothing. If I do have something to say then I'll say it (if it's within reason). That way I'm just neutral to others, and if I appear shy then so be it. I'm in my 30s now and I have learnt through social experience so far that not all NTs are the same, some are shy, awkward or quirky, which could or could not mean autism in disguise. But not every difference in a person means autism. More people aren't autistic than are.
The only problem I have is with the public. I'm never sure who to be when I'm in public places. Strangers hit differently with me, maybe because I've had more bad experiences with strangers than with people I actually know. I have less trust in strangers (nothing personal and not if a stranger is being kind or approachable, either online or offline, so don't take that as a harsh judgement or something).