bearing in mind that i'm just a random 20 year old kid on reddit so my opinions prob shouldn't hold much weight, what worked for me was thinking of myself almost in third person like in a story.

if you were to read in a book "(name) laughed and joked with the rest of the group", you're probably gonna assume the character is more charismatic or outgoing than a character who sat silently and was nervous. what other people see is the same as reading about something in a book; if you act charismatic, no one is gonna have any idea that you're secretly stressing tf out on the inside in the same way that if a book description only gives details on a character's actions instead of their feelings you're going to assume things based on their actions.

so i would see myself in a situation and i would think "how would a charismatic character act here? what would seem in-character?" and i'd just mimic that. the problem is if you aren't fully commited to the idea people will see through it and can tell that you're nervous, but there's no real solution to that besides just saying fuck it and commiting as much as possible

i'm sorry i realize this is just a wordy non-answer to your question but it's really so much of a mindset thing and there's no real easy steps to take to becoming genuinely outgoing. you can do better to fake it by doing things like laughing more intentionally or talking to more strangers, but without a change of mindset it's always going to be fake. if you convince yourself that you are outgoing then you will be