Accept the Self as what you are. Be content with yourself and the present moment and realize they are one and the same. Oops, wrong subreddit. Still applies. Confidence comes when you realize that, because why fear oneself?
Nobody is out of your league unless you think they are my friend. Literally bleed confidence. Body language plays a big part here, so be sure that you know what body language conveys confidence, and display that, smile loads, and MAKE EYE CONTACT. Not psycho staring, just a little linger works. Edit: practice eye contact with everyone you meet. It becomes easier over time.