I think that trying to mimick the tests as close as possible would be helpful, obviously there is limitations on many of them, but the more physical ones can be specifically prepared for.
The equipment carry is the one i found the hardest. Try carrying weights 'farmers walk' style up and down a 25m distance, anything fairly awkward that weighs a bit will help, i think the heaviest weight on this test is around 30k. Wear reasonably heavy clothing and wellies if you can, this may sound silly, but the gear you are wearing makes a hell of a difference when you are actually doing the tests!
make sure you have a good balance between your strength and cardio, the tests require a decent level of both.
if the brigade does a bleep test then practice that. greater manchester used a bleep test instead of the chester step test. i have both on cd, if you want to pm me your address i can send you a copy of either.
most of all listen carefully and put in 110% effort on the day, they are looking out for determined people who dont give up!