It is absolutely impossible for anyone to guide you on the issue when facts and stand taken by the witness are vital. Writing facts, disparities, denials of facts must be noted, and each such cross-examination has to be supported either by documents/exhibits.. Prepare the issues, facts to get admitted and the facts on documents that were denied by the witness and train the advocate. It is an advocate's job, and the presumption is that he is expert in his profession. As a good litigant, one can only supplement the efforts of his advocate.