This coming from a student who is a long way from a dan grade. But my observation thus far having observed people in my own dojo preparing for dan gradings. (our most recent was a nidan test) is that it would be a good idea to know who you will be testing in front of and what they are looking for in a test. Your sensei should know this and help you with preparations. Other than that, just get on the mat and do good aikido.
It will be my sensei who is testing me, and I know he has very different expectations to most people in the organisation. I think I will be more comfortable doing what he wants that with meeting the expectations of anyone else in the organisation.