There are a number of ways to clean an accordion. But the first step is to keep the instrument clean and well looked after in the first place. The exterior can be wiped down after playing to remove sweat and the oil from your skin. Its a simple and easy thing to do.
It is not a good idea to spray cleaners onto an accordion. You do not want the spray to go into places you cannot wipe it off. And it is not a good idea to have cleaning fluids or cream going into the instrument. I wouldn’t use Mr Sheen. A better way to polish the external plastic areas is to use an automotive cleaner polish for plastic (such as Maguires). Put a little onto a cloth, then wipe on. Then wipe off. Leather straps can be waxed with a leather wax nourisher. Wooden sections can be fed with some wood cleaner or oil. (Howards Orange oil used on antiques and furniture is excellent.)
But in doing this cleaning and maintenance, be very sparse with the amount you put on. And do not get it into the accordion. Keeping dust out of the instrument and keeping it in a good temperature and humidity will preserve the instrument, more than anything, in the first place.
As for how to store the instrument. Stand it on its feet. Only exception is an accordion with Cassotto reed blocks, which may sit a different way. In that case you may need to lay the instrument down, so those reeds are vertical.