Carry two detailing rags—one for dirty jobs like sills and the other for detailing the edges of the glass.
Steel wool for tough stains
If you need to remove tree sap, adhesive residue or other tenacious stains from your windows, try #0000 (4 ought) steel wool. Lubricate the glass with a spritz of window cleaner (Windex) and buff away the stains with a wad of super-fine steel wool.
Bring out the power tools
Scrub away the toughest stains on glass with a small buffing wheel and a mild abrasive (Soft Scrub, Bar Keepers Friend or Bon Ami). When you're working near the window sash, protect it with masking tape.