Make sure someone starts it up at least once or twice a week, and revs the engine. If you don't do this, your seals might dry up and then you'll have leakage problems. Also, the tranny seals may be prone to drying up if you don't drive it, so they may want to drive it once in a while around the block and shift through the gears.
If it's been sitting for a long time when you get back, it'll be a good idea to change all fluids. This includes Tranny fluid, oil, and brake fuild (bleed out brakes).
