New blade = no streaks
A 12- to 14-in. squeegee is a good size for most situations. Put in a new rubber blade after each cleaning to prevent streaks.
New blade = no scratches
A razor blade removes paint overspray and gunk. Keep the glass wet and use a new blade each time. Microscopic rust particles on the blade can scratch the glass.
Carry two detailing rags—one for dirty jobs like sills and the other for detailing the edges of the glass.