Study your sectional!!

Obviously it can vary a lot by examiner, but I would say most are
going to really hit you hard on the practical stuff, the useful stuff
that you really should know, and they'll go lighter on the more
extraneous stuff.
Sectional stuff, rules for private pilots (the whole flying for hire,
BFRs, that sort of stuff), airspace (and weather minimums for diff
classes), and general aircraft systems. Be comfortable with the A/C
maintenance logbook as well (flip through the one for the aircraft
youll be using before the test if possible, know where everything is,
make sure its all in order).
Pulling out the trusty ole FAR/AIM certainly cant hurt, but that might
be overkill, know the key sections for sure though (most instructors
will be able to rattle off a handful of sections that are just
generally important to know... 91.103!)

While there are plenty of hardasses out there, most examiners are
pretty good people. Ask instructors to recommend a good one to make
sure you dont get stuck with the one in your area that will stick it
to ya!

Best of luck to ya, its the kind of thing youll do fine on as long as
you care enough to put in the effort, which it seems you are doing.