It is essential for you to answer some questions first. What you have to do is to bring the situation at front, why the break up happened? Whose fault was it? After getting an answer from these questions then only you decide if it is worth to get back your ex or not. Will you be happy with your ex again or getting him/her is just your obsession?
Secondly, think about the lapse of time that you have been separated. This will surely determine if you can still get your ex back fast. Did you maintain communication with him/her or you lost all contact when you broke up? If you didn’t remain in touch then remember that you will first have to establish conversation between both of you again. You just cannot phone someone without any reason, can you?
Once you get back on the friends list of your ex, try to become closer but do not show your desperation of getting back together. Never let him/her know how desperate you are and how much you want him/her in your life again. Don’t turn out to be a spoilt brat, even if your ex is dating some else, be patient and play your moves. Just remember that love does not disappear in a snap. if your ex still loves you, you still have all the chances of getting back together.