The first hurdle in any campaign to win back your ex is figuring out if you even SHOULD try to go through with it. Sometimes you find that your ex is not and will never be willing to give it another try, because he's just not in love with you anymore. There's a pretty easy way to tell, however...which can keep you from stringing yourself along on a lost cause.
The technique for this is as simple as watching how your ex treats the idea of continued communication between the two of you after the breakup, particularly through use of the phone. If he returns all your calls and seems pretty happy to still have you in his life, if only as a friend...then things actually look pretty good for you. He still thinks fondly of you, and within that feeling is the spark of bringing back the flames you both once felt (and you may STILL feel).
It's less encouraging, however, to see that your ex doesn't really want to talk to you anymore. If he pretty much refuses to return any of your calls and getting a hold of him seems impossible...he's either moved on or is trying to move on. That's not necessarily the end of the road for you, but it WILL make things much more difficult to pull together, if indeed they can be salvaged.
The great news is though, that the vast majority of broken relationships can indeed be fixed and become stronger than ever. You just have to know how to read the situation, and above all you need to have a plan.