Determine whether or not your case should be mediated.
A good place to start is for each of you write down what it is you hope to achieve by settling (versus litigating) the matter and then swapping lists at the same time. For any settlement agreement to work, the two of you MUST have at least one goal (hopefully more) in common--whether it's to preserve your friendship/relationship, save money, avoid trial, stay in control of the process, shield your kids from further fighting. . . or maybe you're simply tired of being in court and you both want this over with. Something has to drive the two of you to keep at this difficult task. If you don't value working towards settlement, it WILL fall apart.
Define your issues.
Divorces typically consist of five issues: the children (custody, visitation, and child support), spousal support (also known as alimony), property (anything you own, from the house to the retirements to the pots and pans), debt (anything you own, from the mortgage to credit cards to personal loans), and costs (who pays for the divorce). No couple has the exact same priorities or sensitive spots. You can each create a list of what needs to be resolved in your case and rank these items in order of importance. You could also note how contested or difficult you believe reaching an agreement on that particular item might be. This serves not only to see what the other person values, but also lets you control how intense each discussion is and allow you to prep for such.
Discuss what your mediation needs are.
Depending on your particular issues, you will want to find a mediator who suits your specific needs and wants. For example, if your main issue is that of child custody and visitation, a mediator who is also a licensed therapist or has knowledge of childhood development will have valuable insight for you. On the other hand, if the biggest problem is that of dividing up property one of you owned before marriage and then transferred title into both of your names, you'll want a mediator who is an attorney with experience in this area. The most important thing to remember is that both of you need to feel comfortable with the mediator and confident in his or her abilities to help the two of you through the case.
Be aware of the future.
Divorce is never easy, even if it's something you want. Of course you're angry, hurt, confused, or feeling some other overwhelming combination of emotions. But in order for mediation to be successful, it's important for you to be able to put those feelings in a box at the door and approach your mediation sessions with the utmost professionalism and respect. Treat this process as you would a business transaction, and remember that you are setting yourselves up for the future. If you are able to reach a resolution in the height of your distress, you should be absolutely confident that you will be able to work together in the future to solve any new disputes that may arise. There is nothing more valuable than realizing that the two of you can rise above your differences and cooperate in order to do something that will benefit you and your children in the long run.