I know the answer to this. I think ''just be yourself'' can sometimes mean ''don't act too confident than what you already are.'' It's worked for me.
Once when I went on an employment training course, I knew nobody else in the room. I wanted to fit in and make friends with them, and I suddenly found a way. I knew that just walking in and starting up conversations with people just to look cocky and confident wouldn't work, because I know I will just say the wrong thing and would just start annoying people already. It's no good being something I'm not, because it just does not work. So I just acted shy. I didn't act too shy, where I don't say anything or look at anyone. I still acted friendly, and I smiled a lot, and I made eye-contact to make myself look like I want to be acknowledged, and each time somebody asked me something, I gave a polite response back, and when somebody asked me a friendly question like, ''so where do you live?'', I answered, then asked where they lived. It was quite tricky, but I had to force myself a bit. And I must say, it worked. People in the class liked me, and one of them even asked for my phone number so we could keep in touch. And as the course went on, I grew more and more confident being in their company, and I did say a few more things, only still being a bit shy. But they got used to me being a shy person, and thought nothing of it. They just liked me for who I am. But I knew that if I walked in there trying to look hunky and confident, I will probably come out with stupid things, and I've discovered that NTs do actually notice your ''weirdness'' (weirdness to them) when you try to act more confident than what you are, than if you just be shy but friendly. I know it doesn't sound like it's going to work, but trust me, it does. Starting off being shy is a better way of building your confidence with new people, rather than putting on false confidence then not realising if you make an ass of yourself.
May not work for everyone on the spectrum, but it did for me. Again, it may work depending on the type of environment you're in at the time. A crowded bar won't be very handy, but then again a crowded bar isn't really the right place for Aspies (or anyone shy, for that matter) to want to make friends, but somewhere like a club or a course or something can be more ideal.
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Female