One method I'd suggest is when answering a question is to validate/reference the authority of the answer before you actually get to the crux, for instance if asked about pollution, you might say 'I would take action in accordance the MARPOL regulations, chapter etc, my companies Safety management system etc and that would be...' Immediately you have told the examiner that you know the regulations, you know the publications you refer to, you know the checklists are available, so even if your final answer isn't absolutely comprehensive, you do you know where to find the answers.
Also the proper format for answering orals questions (series of compass bearings, ascertain risk of collision). Practicing the correct format and phraseology that the examiner expects to hear helps you sound more well polished and less likely to dig yourself a hole by saying something wrong.
Do you know what your weak areas were on the last exam? Which Marine Office are you attending?