The sooner you try to win your ex back the better. If you are asking how I get my ex wife back then you might be already divorced and it is going to need an approach that is going to make your ex wife feel special.
You are going to need to have dealt with any obvious problems that caused the split up in the first place. Next you will need to let your wife know that you still love her and want to get back together.
A simple approach that is very effective is to write her a love letter. Women need to feel appreciated in any successful relationship. This is your chance to put it in writing how much you love her and how much you appreciate what she has done for you. Your letter must come from the heart and not be a needy letter begging her to take you back. A hand written letter posted 1st class is the best way to express your love, not texting or an email.
She will appreciate your effort and will not feel threatened.
Women like romantic approaches and because most people are too busy just getting through the week romantic gestures are often the first thing to go in any relationship.
Can you think of a particular romantic gesture that your ex wife would like. Could you recreate your first date, or a special occasion that meant a lot to her? She will often be blown away with something that has special memories for both of you. Even when you break up unless it was a very nasty breakup in which case you would probably not want to get together again, there are always deep feelings that remain.
This is going to give your ex wife a chance to really think about how much she once loved you and could do again.