Hi homonster,
Don't worry too much about maths and physics as they don't crop up in the first stage tests.
Make sure you know the motivation paper material, one girl turned up at my first stage and said she'd not recieved it yet the link to it is at the bottom of the invite e-mail. The other tests are tests that you can't really practice since they test your spacial awareness, number checking ability and ability to follow coded instructions. They're skills that you will either have or don't have so just make sure you're well rested and relaxed because the key is to mix speed with accuracy. Sounds daunting I guess but the first stage is nothing too heavy.
Good luck with it.