The most important thing to remember during the role plays is to keep your cool. The assessors are basically looking to see how you handle the different situations that they throw at you, seeing if you can keep calm under pressure, not panic, not lose your temper and see how good you are at calming other people. One little tip.... the louder they get, the quieter you speak. It works amazing well. To prepare yourself, think about the sort of things the police deal with daily... domestic disturbances, assaults, people taking drugs, traffic accidents, sudden deaths, stop and searches etc and ask yourself, what are you likely to be confronted with (hysterical person, aggresive suspect, vulnerable victim etc) how you would best deal with such a situation, what needs to be done to get the required result. Then you should be more than prepared for the assessments. Good luck!