To person requesting preparation for custody evaluation, I recommend two things. (For the record, the custody recommendation was for me to get 80%; I got 65% signed & entered into the record last week in CA, although the eval took 2 years, all told. I am also a dad, and angry too, despite getting off lucky.) First, find a lawyer who knows local evaluators--- the value a lawyer gives by knowing the people in the trade and what to expect from each far exceeds the value from their knowledge of the law. 2nd, there are two guides that evaluators use as manuals of how to do an evaluation. It is essential to read them dispassionately to get a real idea of what the evaluator looks for, which is very different from what a loving parent looks for. One of them is called Conducting child custody evaluations [by Philip M. Stahl]. I read about 10 books, from parenting to law to tirades, and that was the most useful by far.The author of that book was on a list of court-approved psychological evaluators, but he is really based about 80 miles away and he is booked up months in advance. Having written a couple of books on custody evaluations, the courts treat him as if he has some expertise.
I am not sure that it would have helped me to have read that book, because my court-appointed custody evaluator didn't follow the recommended procedures. But that book does give useful insights into how some custody evaluators see their jobs.