I'd say don't overanalyze the situation.
Focus on you. The buck stops at you.
Focus on your internals. Focus on how you feel...when you wake up...when you eat food...when you go to sleep.
Intend that "Starting now, in my life, I am more confident, more social, more outspoken, more feeling good, and more chill." You don't have to write it down or anything, just affirm it everyday to yourself as a goal. Maybe when you see a group just say that to yourself.
The feeling inside your body dictates EVERYTHING. And by everything I mean how well the interaction goes. So focus on yourself by making yourself feel good in the moment, maybe with some deep, comfortable breaths, and then talk about whatever you want.
"Hey, you guys seemed cool, I had to meet you, I'm *****."
If you also keep in mind, as a beginner, to keep your voice tonality steady or sloping down and not sloping up, you're gold. Gold.
I've dealt with this before. So, keep yourself in a good state, keep even vocal tonality, and talk about whatever you want. I'll leave you with this.
What is your purpose?
Is it to communicate ideas? Convince people? Probably not. When socializing, the purpose is to spread GOOD feelings and have (give) fun. You can only do this if you are feeling good on your own and then spread it to others. It's the only way to do it sustainably, anyway, without neediness or hesitation. So focus on feeling good! Not on what to say. Focus on the communication of that great feeling in your body to others, using words as the medium. I hope one of these images conjured up a positive image of your success. Go with it.
And BTW, unlike with some other areas of PD, I do not feel introspection and meditation without going out will help you. If you do go out, your introspection should focus only a little on practical bits and mostly on making yourself feel good. Going out and feeling good comes first.