Stained Glass: How to care for your panel
Number one rule: Never, never spray window cleaner (or any other cleaner) on your panel. Normal cleaning can be done by running a vacuum brush or dust cloth over it.
If the glass gets dirty, use a soft, clean cloth dampened with glass cleaner. Do not let any 
cleaner drip into the came channels and keep the cloth off the lead as much as possible. Cleaners will eventually dissolve the weatherproofing, which is what cushions and holds the glass in the lead came.
If you want to shine the lead, use a soft, natural brush (like an old-fashioned shoe brush) and vigorously, but lightly buff the came. Use a brush that is clean of any shoe polish, or you'll really make a mess. Brushes that are too stiff will scratch the came, so make sure it's soft.
Storage: The safest place to keep your stained glass panel is hanging in a window. Never lay it flat. That will put undue stress on the glass and may result in a crack or two. If you must store it away, lean it against a wall -- keeping it as upright as possible.