Once you have bladed the soap from the window you will have a small amount of excess liquid along the edge of the glass against the frame. Using the scrim just wipe it away leaving the window completely clear. I prefer Grade 1 scrim other people prefer microfibre cloths, its personal choice. Always keep your scrim as dry as possible otherwise you may get smears, you will also need to boil your scrim for about an hour when you first buy it as it will be very hard and the fibres need working.
Good luck