Go to one of the off-road accessory shops (eg - ARB, ORE, TJM, etc) and grab
a copy of "4WD Days out of Perth".  Cost $12.95.  Has 14 different trips,
most of which you can do in a day.

For a first trip for newbies, the powerline track up behind Mundaring would
do the job.  Starts near Sawyers Valley and runs parallel to the Great
Southern Hwy.  Not too tricky, though has a couple of fun bits.  If ground
clearance is an issue, the more challenging sections have 'gutless' tracks
so you can bypass them if you want.

There is a good hill climb near Mundaring Weir as well, but it's been left
out of the current issue of the book.  You'd need a suspension lift (and a
bit of experience) to get up that one though.

Another easy track is the one from Lancelin to Cervantes.  A few sand hills
and a bit of beach driving.  Is a little bit rocky in parts, but is not too
bad.

Rob