Hot water with either lemon juice or vinegar (lemon juice smells nicer), clean windows, and DRY them after washing, the acidity in vinegar or lemon juice will cut through all grease, and drying will prevent smearing.
I use it on all windows - once worked in a chemist with enormous windows and one of my jobs was washing the windows, we used methalyted spirits in hot water, but if out of meths used the lemon juice or vinegar method with best results.