Only that students should be encouraged to be a little adventurous in their structures. Examiners are always looking for variety, and even if a candidate does not always get something 100% correct, they still get credit for attempting more challenging structures.
Variety could include e.g occasionally putting the subordinate clause ahead of the main clause in a complex sentence.
Perhaps it would be worthwhile reminding students that, while examiners are of course listening for correct verb forms and tenses etc, it is not expected that they always speak in full 100% grammatically correct sentences (as we would, on the other hand, expect in formal Writing).
This all leads me back to a fundamental point which I always stress to students in classes – the need to relax and go into the Speaking interview prepared to engage in a natural way.
Of course, students need to have a broad knowledge of the sorts of questions/topics that may arise and ideas on how to answer, so studying and reading aloud “reference”answers can be useful. Given the nature of the Chinese education system, which still effectively encourages quite a lot of emphasis on rote learning and memorization, the real challenge for teachers, as I see it, is in balancing the student's need for practise with the need to engage naturally in their speaking.
Too much preparation and a concern to introduce a number of set learned phrases and structures in their interview increases many students' anxiety and causes them to get even more stressed if they can't remember them exactly or “lose the thread” in the actual interview. I think it's very worthwhile regularly reminding students that if they have good basic control of grammar and vocabulary, the Speaking interview should not hold any great fears for them.