Firstly, it is obviously helpful to have someone who can practise speaking with you. If you can ask a family member or friend to help, it will make it easier for you. Both of you need to understand the structure of the role play. Make sure that you understand the essentials:
1. It is a test of your ability to explain medical information to a non-medical person. That's why a family member is useful.
2. You have 5 minutes only - time your role play.
3. If you don't have any role play cards to hand - make your own. Imagine a scenario - it may be that you or your partner have experience of a scenario. If not, think of an injury, the treatment for the injury and some of the ways your 'patient' may make things difficult (refuse to follow your advice, become angry because they have waited a long time etc.)
4. If you can't find anyone to help you, use my YouTube videos. Mute the speech, when the nurse speaks. You speak instead. Listen to the patient and respond instead of the nurse on the video.
Finally, make some lists of expressions which might be useful during a role play, e.g. How many different ways can you explain a procedure? (a dressing to do at home, instructions for taking pain relief)