Depends if any predicted grades are/will be based on it if they matter.
Even if they don't matter, treat them like the real exam in terms of how much preparation you do though! Because then once you get to the real exam you'll have learnt the course content once or twice already and so it will all be ezpz and you can understand even the hard stuff.
As for revising, make sure you understand ALL the course content. Once you've done that, do ALL the past papers, marking your papers and making notes of where you go wrong, so you can look at mistakes you keep repeating to prevent yourself doing it again.