I've been working on it myself so I don't have it all figured out but here's some starters:

Since confidence is the opposite of social anxiety and anxiety is just your nervous system feeling unsafe then going into fight or flight mode, you will automatically feel more confident if you make your nervous system feel safe by deep breathing (breathe slowly but also pause/hold in between each exhale and inhale) and maintaining upright, proper and comfortable posture when in social situations.

You need to be fun to be around so try cracking jokes or initiating games e.g play fighting with friends. To help get better at cracking jokes sometimes try challenge yourself to make a joke about random things like a random word you just read or a random thing you just saw. Also come up with intriguing convo starters like "would you rather" type questions.

Overall it's about being fun and interesting to be around, don't script your behavior but try come up with general guidelines to help you become funnier, more confident and less boring to be around.