What's the point of working on your abs if you cant work on your shoulders at the same time? That's what we have always thought, thats why we invented these window wipers to get your shoulders strong and your abs ripped.
Start by the window you need to clean, tighten your abs and lean forward onto the window you want to clean. Now to fire those shoulders start moving your arms around the window to clean the window. As your move your shoulders, make sure you are still leaning against the window and you're keeping your abs tight throughout.