Jenny
When I went for selection I practiced on IQ tests.
WH Smiths sell "Test your own aptitude" by Jim Barret, and"The IQ Booster" by Erwin Brecher" - I found it very useful. Also. exam technique: don't dwell on any Qs that you can't answer quickly - skip them and come back to them later. Finish as many as you can quickly.
I've bought them to prepare for airline interviews having had a ball flying fast things - sometimes with Cubes (Feb 93 NVG).
I can't add anything else to the good advice given already.
Go for it, and if you don't make it, try again - they like that, it shows you're determined and keen.
Otherwise, see you in the civvy world - must get back to my air law!!!
Good luck!