Never refer to the child/ren as "mine" or "yours," and always call them "our" child/ren. If you can't remember this, refer to the kids by name. Mediators like to see parties who acknowledge the other person as a parent. They typically don't care that the other person has never been a part of the children's lives.
Know what will and won't work with your school, work, and other obligations. Don't forget to keep in mind the other parent's schedule. If you leave for work at 4 am, how will you be able to get the children to school? If the other parent has night classes four times a week, who is going to watch the children? Sometimes a 50/50 visitation plan just isn't possible despite your best intentions. It is often times far better for the children to be with a parent rather than with a babysitter.
If your side of the family always gets together Labor Day weekend and you want your child/ren to be a part of this family function every year, you need to be prepared to discuss this. The mediator doesn't know your particular situation, which means that you need to speak up and assert yourself. If your work schedule changes, don't lock yourself into a plan that doesn't accommodate you.
Always go into mediation with firm and well thought out ideas of what you would like as far as a schedule goes, but listen to the other side--you may be pleasantly surprised at the other party's suggestions. The only limit to your schedule is your creativity.
Be a Parent.
At the end of the day, you know your child/ren best. You know what they can and can't handle and what they will or won't like, and you need to make decisions based on that. Some children prefer to go back and forth between two households frequently. Others don't care about the frequency of exchanges so long as there is a set schedule. Take into consideration their age, their personalities, and their needs before anything else.
You may hate the other parent and believe that he or she is a terrible influence on your child/ren. It doesn't matter whether or not you're right. The other parent is likely going to be around your child/ren for the rest of their lives, and a mediation session is not the proper place to name call, bash the other person, or air out your dirty laundry. Instead, focus on the children. You will find that you are much more effective if you are able to do so. For example, instead of saying the other parent never gets the kids to school on time, try saying that you're concerned about the children's excessive number of tardies, since they are beginning to affect their grades. The issue is still addressed, but the other party is less likely to get defensive and sidetracked, and the mediator hears that your concern is the children, not the other person. It takes a little while to get the hang of, but it's a far more successful method than attacking the other party.
At the end of the day, an agreement may not be in your children's best interests. Never agree simply for the sake of making things easier or because you're tired of the mediation process. Think of it this way: if you walk out of a mediation session agreeing to something you don't want, you know you're unhappy. If you leave it up to the judge to decide, you at least have a chance of getting what you want. A mediator's recommendations are, at the end of the day, recommendations. While judges often go with recommendations, they don't always do so, which means that there is a possibility that the judge will agree with your proposed schedule.
Now is not the time to bring up child support, bills, the mortgage, or other such issues. Mediation is about your children. If a discussion regarding child support organically stems from your discussion on visitation, don't be afraid to talk about it. But at the same time, remember that your time is usually best served by addressing as many visitation issues as possible. If you agree to a regular visitation schedule, why not work on a holiday schedule? Why not address transportation issues? How about extracurricular activities?