Use tyre savers to prevent flat spots e.g. Wheel Tyre Saver Stops Flat Spots Caravan Motorhome Campervan Cradle | eBay , use trickle charger for battery maintenance, schedule weekly start and run up to temperature and consider dehumidifying blocks (or similar) for inside cabin if the garage isn't heated.
I wouldnt start and idle - engines dont like it. Might suggest a small desk fan to keep air moving around to prevent damp if its in a cold garage.
If your garage is well ventilated you've got no worries but if it is your typical unheated drafty box - crack the hood to let air circulate.
Don't forget to insure the car whilst stored in case it goes up in smoke!
Also - sorn the car too!