If you need a script the easiest thing to do and understand is that people love to talk about themselves.
1. introduce yourself 2. ask their name 3. ask how they are or how their day is going 4 .... 5. continue to ask them questions as they appropriately come up.
Question 4 can be context dependent.. are you at a party of a mutual friend? Are you at a meetup? Basically use the shared environment to bootstrap the conversation. So a question could be like, "how do you know so and so" etc...
When I feel shy, I always seek out someone else seemingly shy and strike up a conversation that way.
It doesn't have to be perfect. And maybe take a friend with you who has more social awareness to help you. Tell them what your goal is.
Also if someone notices you are blushing and feeling flustered etc.. and asks you what's wrong, just take a breath and say that social situations are difficult for you but you are learning to work through them. Lots of people will be understanding. I say this as an adult. Sometimes you can be around immature folks who do not help the situation but those are people you don't really want to be around anyway.