Well, if you have just broken up, it is best to wait for a while before making your decision.
(To be more precise, just broken up can mean any time from 1 to 30 days. Of course, there are no hard and fast rules. It can also be longer than 30 days, depending on how long you need to take to sort through your feelings.)
Just tell your ex that you need a bit more time before making a decision. If your ex is really serious about getting back together with you, he/she will agree with you. Perhaps, 30 days will be a good period of time. Let your ex knows about it.
What if you have already broken up for quite some time already? Well, if you are still not sure what to do, you can still tell your ex that you need a few days to think about it.
What is important here is to look at your own relationship in an objective manner. What are the underlying problems that cause your break up? Are both of you willing to work through it together?
This is very important. No point getting back together when the root problem is not tackled. It will probably resurface again just after both of you patch up. So, if you want to get an ex back, it is of utmost importance to deal with the underlying problems that causes your break up.
Should I get back together with my ex?
Watch a video that shows you exactly what you must NEVER do, what you should do to get your ex back and why at Should I Get Back Together With My Ex Tips
You will also learn how to reverse the situation if you have already done those things that should NEVER be done.