Be careful about the things one does in response to being insecure. Some people react to the prospect of rejection by giving people a reason to reject them, so that the blow will be softer. That's obviously not a great idea.
It's alright to not be super talkative all the time. Reading up on social norms is probably a good idea if your have autism and find them challenging.
Think about first impression. Keep a good personal hygiene, try to wear clothes that make some sense, try to keep a good posture while not being too "stiff" - let your arms swing while walking and all that. There's a bunch of these tiny things we do that change our perception of each other, and it can be good to be aware.
Keep in mind that you're probably not dealing with a unitary group of people. You're probably not the only person who doesn't have friends yet. And some people will always not like you no matter what - if you have too many friends or are too charismatic, some people will dislike you for that as well. It doesn't matter that some people don't like you, what matters is to find some people one can get along with. Chances are there are people out there with a lot in common with you.