Fear of rejection is a big one, fear of criticism is another.
Then find healthy ways to build up, your worth of self. It's a life job for you, your worth, what you are worth, comes from you and only you.
Remember we are mirrors of each other, what you fear, your fellow human fears as well. To be shy is normal, till you are at-home-in-you. Get into hobbies that you can share with others, if you can share aspects of yourself, then your interests are an avenue to discuss.
You validate you
You complete you
So what if you stumble on words, or what to say. Have a joke or an interesting fact to share.
Have fun, it's not as scary as you think.