Sanding the rims will wear them out a lot faster than they would otherwise have worn out.
You'll probably find that the surface of your brake pads has become fairly hard and smooth/shiny while the bike has been in storage.
Quickest bang for the buck: rough up the surface of the pad with a bit of sandpaper, which you can do without taking them off the bike. If you don't have any sandpaper handy, take the brake pads off and rub them across a concrete surface for the same effect. You want the surface that contacts the rim to not have any gloss or shine at all.