Women are mostly governed by their emotions. Most of the time that is the reason why they might leave a relationship: their emotional needs are not sufficiently met by the man they were together with.
Winning her heart back will require reversing this process. Fair enough… you must show her you are able to address the core of the problem and fulfill the very emotional requirement that she needs to experience, but without just saying with words. Words won’t matter that much, but action.
Firstly, you have to contact her. Start by a phone call or an e-mail, and slowly build contact to more personal and frequent contacts, Just don’t go overboard, make sure it’s a gradual approach. While you are in contact, maintain an attentive attitude, respecting what she has to say and showing that you value it. Staying attentive will help you look for any non-verbal signals she is giving you.
Do not play mind games with her, that’s a lame (and ineffective) approach. Remember, she is one of the few people around you that know you pretty well, so she’ll be able to tell if you are playing games and she is not going to respond well if you are.
You should rather choose a more subtle approach to show her your true intentions. Do not lay your cards on the table bluntly; she must learn about your intentions gradually, and not be confronted with a situation where she would have to say “NO”. So, no pressure.
This way you both will be in the clear about what is going on.
Provide her with an emotional support. Show her you can be the solid “rock” she can lean on if in need. But, do not adopt the position of a friend… Once you have crossed the line that separates friendship from love, there is no going back. Keep a calm and slightly detached attitude, which will allow you to show her empathy, while not allowing you to be overemotional.
Finally, one of the “features” of your personality that will most surely gain her attention is your physical appearance. Don’t forget to keep fit, or improve your shape if you previously let yourself go. She will definitely recognize this positive change.
Winning her heart back is a matter of changing some things about “you” too. Don’t forget the part you have to play and be sure those changes are sustainable before re-approaching her and attempting to salvage the relationship. If you think just one-sided you risk to find more heartache and pain than rescue.