It's a difficult undertaking, to get out there and work your hardest to make things work between you and your ex...winning him back could very well be one of the toughest things you've ever done, but it's also one of the ones you just can't give up on. There are some rules and guidelines though...some dos and some don'ts. Mess up on any of these, and you could be in for a bit harder time than you need to be.
Rule One - Contact: Too much of it is a bad thing...in fact, I recommend to the majority of the people I help that they actually call it complete quits for about a month after the breakup. Being in too close of contact with your ex can cause more friction than you need, as well as make you out to be needy and desperate, even clingy. Cutting off contact not only helps to avoid these things, but it also has several positive benefits as well.
Rule Two - Dating: Don't necessarily knock it as being unloyal or going in the wrong direction. You may be surprised by the benefits of checking out the dating scene. A harmless, shortlived rebound relationship can help you feel a lot better about yourself and remind you that you don't NEED your ex to be happy. Even if you intend to win him back, knowing you don't NEED him gives you a lot of power...power that can be attractive.
Rule Three - Expectations: Don't expect too much out of your ex. He's already presented you with his solution to the problems in your relationship...it's called "the breakup you're struggling to deal with right now." If you want him back, you're going to have to do pretty much all of the work yourself. Nobody said it'd be easy...but with the right plan it can be a lot simpler and less difficult.