What's the best way to store a bicycle for an extended period of time, say 2 months?
Doesn't really matter. Just try to avoid really wet places. I have left bikes in the garage for years. Or for months at a time between rides. (Road bike during the winter, while I ride my MTB to work, and vica versa).
I have left them standing on the floor. Hanging from both wheels in the ceiling. I recall a thread on hanging from just the front wheel and consensus was it did not matter.
Clean the bike, air the tires to a normal pressure, and make sure everything's lubricated that should be. Try to store it in an inside location that you are in every day. Nothing like deciding to get your bike out of storage, only to find that it's missing! If it's going to be sitting on the floor, then some type of cover may be appropriate to keep any dust or dirt away from the bike. If you can secure it with the normal bike lock, that would be an added prevention of theft. After a couple of months, all you should need to do is air up the tires and look forward to a ride.