Give Her Space
When a relationship is ended, tempers are high and people tend to use emotion rather than rationality. Attempting to explain to your ex that breaking up is a mistake would be futile. Give her space to cool down and rethink what had occurred. She will likely replay the event many times in her head and analyze every angle. In the meantime, try to forget your ex. Go out with friends and indulge in your hobbies. You need space as well to consider whether or not you actually want to get back together. Calling or texting immediately after a breakup will only make you appear desperate and insecure, and will diminish your chances of getting her back.
Get Out There
After you have had some time to cool down, get out there and go on a few dates. Visit bars and clubs to flirt with other girls. This will get your mind away from any negative emotions and restore your self-confidence. In addition, your ex is likely to hear word of this from mutual friends and develop a feeling of jealousy. Realizing that she may actually lose you may be the spark to rebuild the lines of communication with you. However, avoid doing this immediately after a breakup as she may view this as a sign that you did not value your relationship with her.
Show Genuine Interest
When you begin speaking with your ex, appear genuinely interested in her and your relationship. Be honest with your feelings and discuss anything that caused the split. You do not want there to be any lingering doubts or feelings of anger when you get back together. Refrain from reuniting the relationship to simply keep her from dating other guys. Both of you must be fully committed to working through your problems and compromising with one another. If either of you is unwilling to change or admit fault, the same arguments will likely resurface repeatedly in the future.
Do not pretend to be different to get a girl back. Either she will see right through you or you will have the same issues in the future. Reconciliation requires a desire to compromise and understand the partner's grievances. Simply pretending to be another person will only delay future fights. If she does not want to get back together after you admitted your faults and agreed to compromise with her, reconsider whether you two should be in a relationship. Many couples reunite simply because it feels comfortable. Analyze whether your personalities complement one another before you get back together.