When I had my selection there I had 3 days notice, no joke.
I have said it, and I will say it again, the aptitude you either have or you don't. you can definitely brush up on your maths, and perhaps do a little hand eye coordination stuff, but the tests are there to judge your underlying ability. I could spend many hours telling you about the ~45-60 mins of intense testing, but your best bet is to just go and see. That being said, I know of a good website that can help you, its the pilotaptitudetest one. you have to pay for it (not much), but it can be useful in helping you brush up on skills.
As for the interview, just go and sell yourself. You can never be sure the questions they will ask, but you can be fairly certain that they will follow the standard competency format, e.g. a lot of questions asking for examples where you have demonstrated your amazing ability. and don't forget to inject at every turn how much you love flying, but also with a focus on commercial flying.
My best advice is to just practice maths and maybe do a few of the pilapt tests, and just have a good think about a WIDE variety of situations where you have shown your ability. And get a really good nights rest. They like to start early. I came from home so had to get up really quite early. Luckily I still passed, but it was a tough old slog.
My final words would be, if you fail the selection, don't give up. they say that they can't offer any feedback, but you will most likely have a good idea on where you may have gone wrong. Then you get another chance, either having to retake everything or maybe just retaking one part. and failing that, I know people who have failed at CTC, and got into OAA, and vice versa.