I think the first question should be, "Why would you want to?" Generally I don't think it is a good idea to get back with an ex but many of you want to, so here are some tips on how to do it.
Desperation is the kiss of death
Girls, you know the most unattractive thing a guy can do is to constantly chase you, tell you how much they love you and basically stalk you. This goes both ways. If you really want to get rid of your ex forever, just keep chasing him and looking desperate.
On the other hand, if you want him to come back, you need to control yourself. Be confident, easy going and cool. Don't let on that you are crushed inside and missing him. In fact it doesn't hurt to casually date other guys. This has a many bonuses for you. It makes you look less concerned that he left. It might make him jealous. Even better yet, you might find you like a different guy and give up on your ex and go on with your life.
Don't sit home and feel sorry for yourself. It doesn't do any good (and it is kind of pathetic). Get out and do all those things you have always wanted to do, but for whatever reason you haven't been doing. Take a class, learn to dance, take up basket weaving. It doesn’t really matter what you do as long as it’s something you want to do and it keeps you busy and it keeps your mind off your ex.
Take care of your looks
Let's face it. Men are visual creatures. If you have gained a few pounds since you started dating him or you stopped dressing up like you used to, this might have something to do with him becoming less interested in you. Get back to being the girl that got him in the first place and you might be able to get him back again. If he is going to be shallow enough that this is going to work, you should really ask yourself if you want him back. Again, I think you are better moving on.
Get your life together
People assume guys want to stay bachelors as long as possible. I don't think this is true. There are plenty of men out there who do want to get married and start a family and they out number the bachelor types. These guys are looking for a mature woman who is ready for the responsibilities of raising a family. If you are the party type, or otherwise have a not so stable lifestyle, you might consider settling down if you want to win him back. On the other hand, you might realize that you just aren't ready for that kind of a relationship. Why change for an ex to try and win him back when you are probably a lot better moving on and finding someone you are compatible with.
Believe it or not, ex boyfriends do sometimes come back. If you had a good relationship to begin with, your ex once thought you were great. It is possible to get that back. Let him know you’re still that same amazing woman and he may just come around. If your relationship wasn't so good, even to begin with, why would you want him back. Relationships end for a reason. It is probably best to move on.