Well, apart from reading as much as you can on this forum, I'd start by starting it from cold, ign. on, wait for the red 'coil' light on the dash to go out, then start it.It should immediately fire up & settle to a smooth tick-over.
While running & doors shut,push the suspension button in the centre-dash, try 'up' first,it should go straight 'up' & the top light will glow, then the bottom one, again, it should drop smoothly & quickly, & again, the lower light will glow. If its slow to rise, then the compressor may be getting 'tired'.
While in neutral, push the 'hi-lo' button, the dash loght 'Low-Range' will light up, then 'Hi' again the light should show 'High'.
try all the windows for normal & 'one-touch', mirrors & isolator switches on the switch-pack.
More difficult will be the heated screens, for, although the dash lights may come on, only a frosty day will show how good it works!!
Take it for a run, enough to get it up to working temp if possible, as most DSE's tend to run BELOW the centre-mark on the gauge.
Check the spare wheel-well for water, another common problem is a leaking boot-seal, resulting in a wet well.
Look under the left seat, & around the carpet-well, this is where the main ECU is located & leaking heater 'o'rings can wet this area & cause nasty electrical probs.
Whith theengine running, switch on the air-con, it should throw out ice-cold air straight away, it wont work at all if theres a leak or the gas is low, then whack it up to 'max' heat, again, if all the flapper-motors are working ok, you will be able to mix & match air-flow from all the outlets.
heck the central-locking works on all doors & tailgate, both remote AND with the key, the No. 2 key would be nice as well!! (only got 1 with mine)
check the rear seat backs unlock & re-lock ok, the buttons on top & very flimsy & I've had to correct both on mine.
there's probably loads more to check, others will soon letv you know, but this will hopefully get you going!!
Good luck.