I certainly will not dispute that Phil makes very very good use of Windex to clean. I have used it too.
there are specialty chemicals available for cleaning surfaces. I have created more problems with some of them than I have solved. The only one I really like is Sikkens Wax and grease remover, ( I seem to recall its M600 ?) That said, when I have a surface ready to spray,, then get all my color on it, I really try hard not to touch it with anything at all prior to clearing it. If I feel the need to, I will use a water based cleaner, or windex,, ( this by the way is in a commercial enviroment) certain products I have never trusted, PPG DX 330 is one that comes to mind, has given me FITS.
ONe thing people dont understand about "cleaning for paint' is that you need to envision the contaminants as tiny ball bearings. visualize dropping a gallon jug of ball bearings on a gym floor, then try to sweep them up..The only way to really clean a surface is to flood it with a generous amount of liquid cleaner,, enough to float the contaminants ( emulsifying those that need dissolving) and then with LOTS of lint free paper towels, wipe the liquid OFF the edge of a surface, pushing all the contaminants off like you were squeegying the ball bearings off the gym floor.