How to win her back

To get her back isn't going to be very easy you need to be at the top of your game and you need God's intervion because if it's not meant to be, you can try and try and still will not get her back.
Also, you have to make her want you, show how much you've changed, and then make the move.

Give her some space. 

• The first thing you need to do is give the girl some space. If you start knocking down her door and calling her every five minutes she'll only pull further away from you. The amount of space and time you give her depends on what happened when you tried to date her.
• If you ended a serious relationship, you'll need to give her more space than you would if you had just dated a few times.
• If you see her socially, be polite and say hi, but make it clear that you're not going to bother her.
• If your relationship ended because she was so jealous that you were always hanging around with other girls, then you shouldn't make her jealous or she'll just be reminded of the reason why things didn't work out between you. But if your relationship ended because she thought you were just too into her, or that she was bored by you, then making her jealous is a great move. Here's how to do it:

If you're on speaking terms, casually mention other girls. You can mention one girl a few times, leading her to wonder, "Who is this girl?" Or you can just talk about a group of girls, mentioning that you were at a party that was filled with mostly girls but that you were "okay with that."
Don't overdo it.
If she hears you talking about other girls and sees you flirting with others, she may want you even more, but if you're all over every girl at every party, you may look desperate or sleazy.

Showing Her How Much You've Changed
 If you broke up because she felt that you didn't give her enough affection or time or that you spent too much time flirting with other women, it's time to do the exact opposite and to make yourself available to her and have no other women on your radar.
...Show her that your schedule is free and that you're up for hanging out whenever. She'll no longer have to hang out with you during the one hour you're free.

• Don't make her jealous. In your case, you should stay away from the other ladies as much as possible to show that you only have eyes for her.
• Take the time to listen. If she thought you didn't care about her feelings before, maintain eye contact and let her talk without interrupting.
• If you hurt her, apologize. If you really want her back, you have to be the man and apologize for what went wrong. If she was hurt by you, she'll want to stay away from you for fear of getting hurt again. So man up and tell her you made a mistake.

Make sure to do this in person. It won't do if you just send her a text message or an e-mail; it has to be in person otherwise she will see that you are not very serious about this apology and so she won't take it seriously either. So own up and go apologise for what you did to her.

• Don't be disappointed if she doesn't accept your apology right away. If she doesn't accept it, she's probably still working through what happened but still appreciates your effort. Just say, "You can't blame me for trying" instead of arguing her into accepting your apology.
• Show what a better, more mature person you've become. She should be able to see how much you've changed without you having to say it yourself or to convince her that you're completely different. Face it -- many girls are more mature than their male counterparts, so wow her with your ability to be rational and mature.
• Don't be jealous. Don't ask her about that guy she's been talking to; this will only encourage her to talk to him more, and will make you look insecure for caring.

Open up to her,Tell her how you feel. 
Once she wants you a bit more and can see that you're a different person, it's time to stop playing games and to tell her how you really feel. How else can you get the ball rolling? If it ended badly, she's not going to ask you to pick things up again, so you need to get your act together and open up.

• Tell her at the right place and time. Pick a time when she's not too busy and you can be alone, ideally at night or in a semi-secluded location.
• Maintain eye contact when you tell herNo looking around, no checking your phone.No more Mr. Tough Guy. It's time to be open and honest and to share your true feelings.

First, acknowledge what went wrong, and apologize for it again if you haven't already. Then, tell her how much you've changed and how much you'd love to give it another try.
Say, "I can't believe what an idiot I've been. You were the best thing that ever happened to me and I really screwed it up. Let me make it up to you."
Keep the girl this time.
If everything goes on well,Remind yourself what happened the last time, and vow not to do it again.
Look at it as starting fresh. You don't have to rehash the old relationship, but work on building something completely new and much better.
Relax. Just enjoy being with the girl instead of worrying about not screwing up again all the time.