I park mine for the winter too, and just take it out on nice days. Last year it went for 3 months without moving.
A winter period isnt really that long, so dont worry too much.
If you are not driving the car at all, then I would at least roll it back and forth in the garage so that the tyres dont get flat spots.
If you start it, drive it, and give it a decent run. I dont think starting cars in garages and letting them idle for 20mins does them any good at all.
Get a trickle charger. Theres nothing more annoying than waking up to good weather, jumping in the car and finding the bugger wont start!! Mine cost £20 and has been perfect, keeps the battery in good shape and ensures its always ready to go.
IF you have a Spider, be careful with the roof. The rear window is very sensitive to cracking when the plastic is cold (and brittle).
-1998 916 Spider 2.0TS Lusso-
H&S Corse stage 1.
CATCAMs stage 1 cams with Savali custom ECU remap.
305mm discs with 166 4-pot callipers.
Ragazzon exhaust mid section.
Biscione Racing 2x70mm rear section.
17" Zender Siena wheels with 3mm rear spacers.
etc etc etc!