There are many factors to consider when selecting a storage site. First, choose an area that is out of direct sunlight, as UV rays can damage paint, plastic and leather. Also, pick an area that doesn't have large temperature fluctuations, and is cool and dry. Your storage area should be free of mice. If you're not sure that it is, put some traps or poison underneath the bike.
Mice love airboxes and the taste of wiring harnesses.
Also, select a low-traffic area where your bike isn't going to be bumped into by you or anyone else on a regular basis. Next, throw a cover over your bike. Many people believe a plastic tarp is best, as it keeps moisture out. But the problem with these tarps is that they don't breathe. Moisture in the air gets trapped underneath and builds up until it falls on the bike, causing corrosion.