There's not a lot you can prepare with.
From what I was told/read, there's a few parts for stage 1a.
you've got an English listening test, English grammer test - try listening to online radio stations of various nations if you need to, to understand the various national accents.
Aptitude testing - from what I've read is about hand-eye co-ordination and psychomotor skills.
Reasoning test - 3D shapes (I think). if you can find a test paper for these then study it.
Finally the presentation.