The first step towards getting your beloved back is to leave her alone for a while to allow her to take a well thought out decision. Nagging and pestering would only increase the distance between you. Being separated and still holding love for her on your mind could be a hard wicket to be in. However, haste has no role. If your ex also harbors love and affection for you, she might reciprocate if given proper time and space.
The fact is that a majority of break ups can be reversed, if you have the will to work it out systematically. Take a closer look at the factors that could have resulted in the breakup; learn from the mistake and try not to repeat it.
Make sure that you portray yourself as a confident and strong person and not someone who is desperate to win the ex back (though in reality it could well be a reality) seeming apprehensive and doubtful will only push your ex further away. However make sure that you do not do overboard and over do it by making your ex jealous as it could be very well the last nail on your coffin. Instead you want him to feel that his presence is simply irreplaceable and that he was the best part of your life. Enhance his confidence without seeming desperate and needy to put across the point that you make a wonderful pair together irrespective of the minor differences that existed in your lives. If you find out that he is involved with some one else, you cannot do pretty much anything and there is no point in getting upset.