Good work, if i read your post right you are waiting for your assesement day?
(can i ask what band u got for spec testing?)
If so they would have already given/told you about the timings and content of the day which is a medical, and 2 interview(i think), one with a pysch and the other with a DF recuriiter. One thing to remember is that the DF member can overrule the head doctor.
To impress the DFR u have to have a indepth knowledge of what position u want and the responibilites including secondary duties, posting locations, training bases and lengths(You should know each step of the way in depth by now, etc.
There's not much to say about the pysch, you have to be yourself and answer the questions truthfully, they will pick out liers straight away.
Have a good knowledge of military lifestyle and try to talk to some ppl already "In", of varying occupations
It also helps to have a basic understanding of the other forces and what they are comprised of to show that if u are offered Army or Navy that u already have some basic knowledge.
I'll PM u with some other hint and tips for flight screening and what not.
Good luck mate.