I didn't do CAFS, but I've had a look at some past papers and solutions, and picked up on a few things.
To be honest, I don't really like the NESA sample answers, as in my opinion, they aren't strong Band 6 level. The issue is that with some of the answers, there isn't enough detail. I think that since you mentioned you have understood the content thoroughly, all you have to maintain is that extra level of refinement or sophistication in your answers. Essentially, you want to give markers good reasons to reward you with high marks. With any subject which has short answer questions (I'll use Chemistry as an example), it's very important to not only link to the general topic, but to link it to specific key words in the syllabus which are relevant to the question. Most importantly, have a clear and concise structure with your answer which makes it very easy for markers to read along and follow.
