Apart from the obvious step of doing the CAE's OET preparation course, candidates should be reading professional literature and possibly some popular science. I assume the listening would be of a diagnosis, but again practice makes perfect. I think sample practice tests from OET website might not enough for you. And recently, many students ask me to provide some OET materials. However, I only have the official OET practice materials and due to copyright issue, I cannot provide it on public domain – my blog.
With speaking, my advice would be that you should know how to put medical jargon in every day English – that's very important. With writing, read the task very carefully, noting who exactly you are writing to and why. Apart from that it's a case of 'less is more' – ie don't just write out the material you've been given.