If you are in the throes of a broken relationship, you need to think very carefully about your ex and your relationship before doing anything.
Then, if after careful consideration you are sure you want to win your ex back, you need to decide what action you need to take.
Here are some brief suggestions of ways which will give you a positive start.
First of all you need to realise that you cannot simply turn love on and off at will.
So that love might not be lost at all, which should certainly work in your favour.
If you believe that you were in any way responsible for the break up, then APOLOGISE.
You may consider that you have already apologised, maybe several times, but your ex may have thought that your apology was simply a ploy to avoid separation.
Apologising again, when you seemingly have nothing to gain should convince your ex that you are sincere.
If however, it was the action(s) of your ex that caused the split, instead of seeking an apology from them, FORGIVE THEM.
This may be very difficult to do but is a very powerful step.
Your forgiveness must be sincere however, because if you haven't really forgiven the other person for whatever was done, then later on, old wounds may be reopened and it's likely that hurtful things will be said again.
Finally, to win back lost love, you really need to show the other person the "YOU" they fell in love with and remind them gently that they were with you because of your "good qualities" and not because you're angry, jealous or hurt.
You might not be able to hide the hurt, but concentrate on being the best "you" you can possibly be.
You might well win your ex back by simply reminding them why they loved you in the first place.