what should my someone do during the child support case so he wont loose the case?

The question is, what does "losing the case" mean to you?  In New York State, the law is very clear about what the obligation is to pay child support.  So your question should not be about how to win or lose a child support case, but what to do to ensure that the court orders what is fair and reasonable according to the statute.   Ultimately, you should plan on bringing tax returns and W2's for 2010, 2011 and 2012; your last three pay stubs from employment; proof of any other child support or alimony order; proof of any payments you made to the other parent for the child if you are not the custodial parent.   If there are specific issues relevant to your case in particular that you believe should be brought up in court, you should speak to an attorney to discuss your rights.