How can I be less uptight?

[ThisMomentIsReal]

Hi everyone,
I would really appreciate some advice.
When I was younger, I was bullied in school, then was in an abusive relationship in early adulthood. I used to be a people-pleaser and a "doormat."
I really worked hard to try to rebuild myself and read some very helpful books, but I now seem to have the opposite problem. When I meet new people, I can easily find something I dislike about them even if I don't want this to happen (perhaps because I worry about getting hurt again?) I'm more vocal about my opinions but that's not always a good thing. I find myself probably (over)-reacting to people who are short-tempered whereas before I was scared to.
If anybody asks me to do something and it's not work-related or someone I'm close to, I am now very reluctant to do it because I feel like doing what someone asks is essentially allowing them to walk over me.
I would appreciate some advice on how to achieve a middle ground.
Thanks!

Take a minute to ask yourself, "Am I being a dick about this?"
If not, crack on.
Sometimes this may involve briefly explaining your "no" ("I can see you're a bit stuck but I'm really busy that week") or diplomatically wielding a "not at the moment I'm afraid" or similar instead.

Re your reactions to people - just remind yourself you don't know what's going on in people's lives, and cut them a bit of slack. Not a lot - just a little - such as "not catching" rude outbursts.
You're not obligated to like people though OP ! A bit of reading up on why we get the first impressions we do, of people, might help. Things like, we might find X annoying because they look a lot like old enemy Y, or because they are too much like ourselves and are unconsciously barging in on "our" spot in the conversation and social group - stuff like that.

Then you can get a clearer view on whether a person is, you know, actually OK but just rubs you up the wrong way through no fault of their own, or is just so different a person that you have 0 in common, or is definitely untrustworthy in some way so that you do need to limit your involvement with them. But then you at least understand what's going on IYSWIM.

Just to add: I was raised to have a positive attitude and look on the bright side, so I'd consider myself somewhat positive but somewhat negative due to the above. I can fake it but I know when I am enjoying something or someone's company, and when it's a stretch.

InTheWain what great advice. Don't think I can put it any better.
Do you have a trusted person you can reality check yourself with. Just to ring stuff past them and check if you did overreact, someone whose opinion you trust to help you calibrate yourself.

Thanks so much for your advice, Inthewainscoting (I cross-posted my last comment). It definitely gives me something to think about. That is a good question to ask myself.

Hi TopCatsTopHat,
Yes, I could reality check with my parents. My DM especially is good about being honest and not beating around the bush. I try not to bother them too much because they are overstretched at the moment, but they would help with that if I asked them.