Well, you are on the first step which is admitting that you still have feelings for your partner and though you are already not linked together, there still are ways by which you could win her back. To start with, you have to say to yourself that you have already split up and you do not have control to what the other has to say so you have to respect the decision. You just have to give it your all, actually. Do things better this time. Avoid what things spark arguments.