How do you approach new people?

so I really like this girl, but have never approached her. I see her whenever I least expect it. I saw her first at my little brother's football practice, but only once, and then I was working one day, and I saw her there, and then I started going to church again, and, of course, she's there. She came to one of the varsity lacrosse games (I was playing) and I spotted her right away in the full grandstands, smiled, and she smiled too. I always chicken out and dont talk to her, and then afterward promise myself I wont anymore. i cant help it. I've always been the shy, keep to myself kind of guy. I want to change that, but idk how. I feel like im always being negatively judged, maybe cause nobody really ever compliments me, and I only hear insults from people, but thats a whole nother story