First and the most important thing you should think about is the REASON of your break-up.If you are realising the reason behindthebreak-up & which you are not going to blame on her then this means you strongly wants your ex girlfriend back in your life.If you are at fault then acknowledging this and taking responsibility is a great first step & you must correct whatever you mistakes you did in the past & improve yourself so that you can be mptable by your ex.
Second,you should not beg to your ex to come back into your life again.Begging to partner can make things worse for you.Instead of begging try to convince her that now you have changed,your way of thinking about her is changed & you are ready to do anything improve things between you and her.After this,give her some time like few weeks to think about it & to get past the emotional aspect of breaking up.
Third,while she is thinking during that time period you should talk with her friends or family members.Don’t get too much stressed about this.Get out and enjoy yourself with your friends as this will help heal you. Sitting at home worrying and thinking about your break up will only make it worse.
Fourth,you can call her or message her but keep the conversation short and saou must go.If you think at any point of conversation that she wants to talk more then just hang in there for some more time.Tell her sorry for whatever mistakes you have done(if you were at fault) & during that time you were not able to understand what exactly you were doing.Talk with her like this every so often as long as she does not cut you off and hopefully the two of you will start to get closer again & live a beautiful life.