To remarry your ex certainly requires much forethought. There are many who have done it and many more are sure to follow in their footsteps. Sometimes it lasts, other times it doesn't. Richard Burton and Liz Taylor did it and you know how that turned out -- it didn't work.
Give it time. When you remarry, time is a major factor. If you make decisions on the rebound, they most likely will not be sound. Time is needed to heal from emotional wounds of the past. Also, when you first separate, there is the loneliness factor; you may remarry due to being lonely, which is not a good reason and unwise. Confront and resolve past issues. If you can't do this, don't remarry; otherwise, it's guaranteed to fail. Time, in this case, can work against you because you may forget the pain of the past. Don't harp on it, but don't allow it to slide either.
Be honest and don't hide anything. When you plan to remarry an ex, deception and manipulation must go. You both know each other very well, so the other one will perceive you have not changed and may back out. Don't underestimate your ex; she may know you better than you think. Build trust. More than likely, things happened to destroy trust between you and the ex. Trust is extremely important; if you ex doesn't trust you (or you don't trust him), then there's not much chance of remarriage working. Actions speak louder than words. Therefore, make a special effort to show your ex that you're worthy of his trust.
Consider the kids if you have any. However, do not remarry just for them. If you're uncertain of remarriage, don't give the kids false hope. It may be wise to keep it a secret from them until you're positive. They already have emotional damage from the divorce and there is no need to add to it. Accept responsibility for your part in the breakup. When couples remarry, the blame game needs to stop! Be realistic and know that nobody is perfect. Instead, develop better communication skills to resolve issues.
Seek marriage counseling, both jointly and separately. It's also a good idea to take marriage classes and consider a marriage retreat within a group setting. If you seriously want to remarry and make it work, go all out! Lastly, if you make reconciliation a priority, the remarriage will stand a good chance of making it. After all, every relationships requires effort.