The Introvert has a harder path towards being attractive to others on a massive level and in having high quality relationships if only for the fact that there tends to be a much smaller pool to choose from. From the outside, the issue often seems to be one of confidence and lackthereof. Getting pumped up does work to an extent, but you often feel like your confidence is on a ticking bomb and you have to get it all out before it blows up and you're left with nothing.
The only thing that will give you that Holy Grail of confidence--where it's not liquor infused, it isn't temporary from a great pep talk, it isn't something you're constantly having to try to force out is if you don't care anymore. Great revelation, but one many have already reached. What's the million dollar question?
HOW THE HELL DO I STOP CARING?!
It's very human and natural to care what others think. It's ingrained into our survival instincts. If we didn't have very accepting parents, it can make us even more unsure of ourselves. If we are big thinkers, we can't often come to the conclusion that some people don't like us and that can lead to insecurity as well.
First, realize you are getting something out of caring or at least you're trying to...you're getting sex you hope or you're getting people to think you're cool or you're avoiding embarresing yourself or saying something stupid that you get mocked for later or you typically hurt people's feelings when you take your filter off and you reason that it's better to just talk rather than learn how to be nice to people. Realize that unless you're ultimately ok with a life where none of that is in your control and, in fact, will happen quite often then you are not ready to learn not to care. A big objection comes when we bring up work--where we spend the majority of our lives. I would say don't use this as an excuse to care what other things. Rather, have a line of professionalism that you adhere to when it's appropriate but, at the same time, you know people aren't holding things against you and don't care if they do as long as it's not about your work or professionalism.
Second, commit to the goal and have a vision of it. Think about the type of person you are when you don't care about being judged. Maybe the only place this is is alone. This can be your goal. See people in your life that have that lack of caring and also look to them as the goal of where you'll get to.
Third, realize that not caring is a difficult skill as long as you have something to lose and you will have to work at it. There's a reason guys who go out into the world and resolve to become doctors and layers and get a decent wife who has that sexual night with the bartender she met out with her girlfriends behind the bar next to the dumpster are actually inferior in certain ways than guys with fat guts but honestly don't care and get laid countlessly by girls that they themselves would admit are way hotter than them. It's more than just letting go--it's a skill. It's an unnatural level of certainty in yourself and ability to be yourself regardless of people judging you. It will take time. It will be a lot of progress and falling backwards and having to keep going as you slowly but surely learn to just be you even in high social pressure situations.
Fourth, the real secret is that they don't care whether or not they get what they want. That's where that nice push and pull comes in. They may make moves on the girl but it's the not caring really if they actually get to have sex with her or not that has gives off that highly attractive cool guy i'd like to sleep with personality vibe. If you are with a new group of friends and one guy is clearly the leader/alpha of the group then the guy who effortlessly makes himself one of the most fun guys of the group really does not care about any of their opinions of him. Whether he plays football or reads comic books that 0% give a s*** is what makes him fun to be around. And I can't stress enough the 0% when it comes to girls especially. Girls tend to be better than guys at smelling bs so you can't just care but want to not care...you really have to not care and that comes from being ok with not getting to have sex. The charismatic guy can still be annoying if he's pawing her constantly to come home with him as if he can't read social cues. Let her feel it off you that you don't really care if you don't get it and then you get it. It's the biggest mind f*** but my god does it work...
Finally, realize it's not just for others benefit but for you as well. Obviously you're not changing because you're too stifled with yourself--you're oding it because you're this stilted person around other people and often no fun. So you let out your personality and people have a lot of fun around you. Giving value you is great and you always get back what you put out but also be motivated by the fact that you will enjoy yourself and your life much more when you're no longer burdened by the opinions of others. It's like going to the gym to get abs and then starting to enjoy the healthier diet you started to get them. It is a world free of social anxieties it is a world free of needing to last a certain amount of time have a certain length or girth be funny or interesting enough be nice enough but also have an edge look good make enough money NONE of that will matter once you stop care about "winning" by charming others with a fake, stilted personality and by biting your tongue.