Be one with GN3, get the terminology down to a tee and be able to write detailed descriptions of how to carry out ring finals, Zs testing, earth electrode testing, insulation resistance testing and the 3 different types of supply all with expected values, diagrams etc as atleast one of these will come up on your written and will be worth a large amount of your marks and will eat into your time in a big way so bullet points are the way forward and don't ramble either