Firstly congrats on getting the CPL skills test out of the way.
I am still doing the I/R but I started without any real clue of what was ahead , other than I had heard the horror stories!
It has been , at least, so far quite an enjoyable experiance.
I use Rant , which has been a great help for the routes and holds.
Its quite basic graphically but dont be fooled, it is a very clever program, for example it accounts for wind and dip.
I find it helps going into the sim knowing what to expect from a situational awareness perspective and rant seems to assist with that.
As for pre reading and the like , I would have a look at the holds, the different methods of entry, the effects of wind etc.
Other than that you might find it helpful to get hold of the SID from wherever you are going to be doing your test from, some STARs, ILS and NDB approach charts.
On the subject of charts, if you still have your black jeppy book as used in your flight planning exam, get to know the above named charts well, and practice self briefing them from top to bottom as if you were going to use them for real.
As I said I am only a student, you might bet some better advice from an I/R instructor.
Good luck and enjoy .
Flyfish