How do you go about winning someone you previously lost? I keep getting the impression the way is still open but I don't know how to overcome the initial fear of taking the next step?
Whether there's even a chance of you winning someone back will be entirely dependent on why things ended and how they ended.
Give her space and be patient. Connect occasionally with kindness and on topics you've always had in common. You can send a card at Christmas and on her birthday, but nothing too mushy. Skip Valentine's Day unless it's just a friend card. I might let her know I'm missing her and still think of her fondly. From experience, I'll say you may very well win her back as a friend, but maybe not as a lover. If you can't handle that, then try to move on.