Better preparation for your expectations. Often parties/lawyers come to the mediation expecting the other side to realize the strength & merit of their position, only to become frustrated upon receiving offers in numbers that reflect the opposite. Some tips:
(1) before mediation, share information with one another; try to understand & prepare your client to understand their position (however distasteful that feels);
(2) where the other side bases its position on misinformation, don't wait for mediation to "spring" it; instead, educate them. Equally if not more important to preparing the lawyers, is helping them prepare their client or adjuster or other decision makers in advance so they can better prepare.
(3) Be prepared to discuss w/the mediator your case weaknesses & responses to the other side's points, & give ammunition to help or redirect to stronger points;
(4) reasonable case valuation: don't just rely on the highest or lowest verdicts, do a well rounded assessment of potential outcomes. It will help your client's expectations, & perhaps your own.