I get how you feel. Sometimes I find it helps to look them in the eyes and stand straight, just to seem less shy. Obviously don't pierce a hole through their skull but just assert yourself and realize that you're awesome and can talk to anyone.
It can be a battle with anxiety though I'll give you that.
Feeling nervous when talking to strangers is normal , once you get to know the person you will be comfortable around them and then the conversation will be smooth. Try to make the conversation interesting. You can start off with likes/interest it will be a bonus if the other person had the same interest.
It's important to not get too caught up in your insecurities. When you're anxious in your mind, it'll come out. I know it's hard to just relax, but not making a convo a big deal and make it easier to start it.