Most Helpful Guy
Sounds really cliché, but be yourself. If you are fine with who you are and what you look like, others will as well. Just find some things which you are proud of or strongly like, perhaps even something which really sets you apart from others. Enhance these features about yourself, or 'build your personality' around them and step up to girls.
Don't be afraid to walk to a girl if you're for example in a train. The worst that can happen is she totally ignores you or asks you to go away, but you'll likely never see her ever again. The best that could happen is a relationship.