Hi there,
Happy new year! Congratulations for receiving an invite from OAA Luke! I was successful with the generation easyJet OAA assessment late last year, so I feel I could be in a position to help you out with your prep!
If I'm totally honest, there really isn't a whole lot you can do to prepare for the day. I would wholeheartedly recommend spending lots of time going through some gcse maths and physics revision though, so if you still have your textbook, have access to BBC bitesize or even CAE's own Physics prep pack (at a cost, but well worth the investment), you should be in a prime position to do well. There really isn't anything too surprising in the tests.
Keeping a cool head and avoiding getting flustered is important in order to do well in these aptitude assessments as it not only gives you a clear mind to work with, but it may also allow you to actually enjoy some of the tests! Practicing with some pilot aptitude software, such as latestpilotjobs and skytest, practicing with a joystick if you have a flight sim, etc will undoubtedly help you achieve that!
Best of luck! Send me a pm if you have any other questions.