There are many ways that can be used to get your ex back if you have broken up with them. Some of these are useless and will not work because they are making you be overly pushy. Being pushy in your pursuit of getting your ex back will doom you to failure at different levels.
First, if your ex left you it was for a reason and they did it voluntarily. If you were to be pushy with them to convince them that they should come back, they will only get further away. They left on their own for a reason and will only come back on their own. Second, if you did talk them into coming back, maybe against their will, the relationship is doomed to fail again.
That leaves you with resisting your natural instincts and giving your ex some space. Hold back from chasing after them and try a technique that will allow your ex to make the choice to come back on their own. When they have made their own decision, you will find your ability to begin a new relationship will be much better.
One way to get them to make this choice on their own is to change their opinion of you. Take a look at the person you were when the two of you first started dating and look at what you were like when you broke up. Your goal would be to let them see the person they fell for when they first met you. When they become attracted and interested in you again there will be a chance of wanting you back.