Mediation normally means they try to get one person to change their requests so it doesn't go to court for a decision. Decide before hand what you actually have to have, what you are willing to negotiate on and what you really don't care about.
Also, understand the law so that you are not asking for something that the law says you can't do - such as I will only give you $50/week for CS when the law says it is $100/week.
Also, you may want to give us a few details of things you want so that we can tell you if you are off base. One person who was on this site was not agreeable to 50/50 - went to mediation saying she would not consider 50/50 - lost her kids because the spouse ended up looking "more reasonable". While this is only temporary orders right now, courts tend to go with the "status quo" and she may never even get 50/50, much less full custody now.
So, if you want 50/50 custody, ask for full custody. They come back and say 50/50, you agree. That way you look like a reasonable person and yet, you got what you were asking for. If you ask for 50/50, they are going to come back with the standard visitation time - EOWE. You have no negotiation room. Also, be sure what you are asking for is what you are able to do. If you are asking 50/50, can you take care of the kids 50% of time with your work schedule, travel schedule, school schedule?
Also, understand that you can save big bucks if things are decided in mediation. If it goes to court, a stranger (the judge) is going to make the decision and neither of you may be happy - actually neither of you should be happy - that means no one was a "winner" or a "loser".