An empty fuel tank will develop condensation. Fill to the brim when storing. It'll be lousy when you do come to use it again and you'll have to add some additive to bring the octane value up again, but better than a rusty tank.
This was the advice given to us by the REME mechanics when we went off on 6 and 12 month tours and I've seen plenty if advice on other car forums to back it up.
When I had my Mustang, I only ran it during the Summer, so it was stored for as much as 8 months at a time some years. I used a Black & Decker trickle charger attached to the battery to keep the electrics from dying.
If you can run the engine once a month for an hour or two that'll keep the oil circulating and prevent seizing and stop the seals drying up. Run the A/C at the same time for at least 40 minutes a month. Stick a hose on the exhaust and run it out of a window or door otherwise loads of particulate crap will settle in the garage...
If you don't jack it up on stands, put a double layer of carpet off-cut under each wheel to help prevent flat spots. Personally I'd take the wheels off if it were standing for more than 6 months. I've twice had to replace tyres on my Cougar that were killed by being stored outside through the winter months, whereas the Mustang tyres lasted 7 years by being on carpet in a garage.
