I found the Distance Speed Time calcs from page 109 of this thread really helpful to sharpen up as the numerical test is based on them in different variations. Try to calculate distances between two points based on time travelled at certain speeds etc too.
Cube test was by the far hardest out of all of them so the more you practise the better, though like everyone says finding examples is hard and staring at them for too long just makes it harder in my opinion.