I worked on my quickfire maths for quite some time before. Speed, dist, time etc - lived and breathed those kind of calculations for weeks.
I had been on the UAS for a year or so before going to OASC so already had a good idea of what to expect. I finished the aptitude tests very quickly compared to others and found out much later that I had come out with very high scores - which did not reflect my aptitude level, but my swotting up. I also used to (rather geeky but very useful) use Microsoft Flight Simulator which, at the time, had just come out with add on packs photorealistic scenery, allowing me to navigate between known places. I'd hammer the flight sim, constantly doing calculations in my head, and re-doing UAS flying sorties (navigation, diversion, EFATO etc etc).
Helped my UAS flying and aptitude tests a lot. A good few years ago mind.
All the best!!!