As for the NSAA question papers themselves, I'd do them under strict time limits so you get used to the timing of the exam and the pace you need to be working at. This year, for example, lots of people (myself included) weren't able to finish the paper on time because of the time limits. Also make sure you're marking the papers you do and taking them to teachers to go through (especially the questions you found challenging) so that you're learning from your mistakes.
Just got my AS results and got AAAA, I will be applying to Cambridge to natural sciences in October. Is there any advice for how I should prepare for the exam because there aren't many past papers available. Also, does anyone have a link to the NSAA spec?
Also make sure you read the specifications (https://www.undergraduate.study.cam....ation_2018.pdf, although I don't think it's up yet) so you know what the required knowledge is. T.