Window cleaning checklist
How to clean windows without streaks: when to do it, what to use, in what order, and what to do about frames, seals and drainage slots. The list adapts to your windows.

[ ] Pick an overcast, still day
    In sun or wind the solution dries before the squeegee gets there and leaves lines. If you cannot wait for the weather, clean the window while it is in shade.
[ ] Get out a squeegee, microfibre cloths and a channel brush
    You need a squeegee with an undamaged blade, a cloth for washing, a dry one for the edges, a non-scratch sponge and a bucket. Check the blade: a nicked one leaves a line behind it.
[ ] Clear the sill and take down the curtains
    Move plants, electronics and clutter so you are not working around them with wet hands. The curtains can go to the wash while you are at it.
[ ] Brush the frame, sashes and channels dry
    This is the step that decides whether you get streaks. Dry dust from the channels turns to slurry and spreads across the whole pane.
[ ] Wash the frame and sashes
    Use a soft sponge and a mild cleaner: abrasives and harsh chemicals leave dull marks on the frame that cannot be removed.
[ ] Wipe the seals without stretching them
    Remove dust gently with a damp cloth and dry it. A stretched or dried-out seal loses heat and lets noise in.
[ ] Clear the drainage slots at the bottom of the frame
    They let water out of the profile. Blocked slots cause a puddle on the sill and damp that gets mistaken for a leak.
[ ] Wet the glass with solution, top to bottom
    Do not skimp on water: dry grit under the sponge scratches the glass. Cover the whole surface, including corners and edges.
[ ] Squeegee the water off in overlapping strokes
    Work from the top down, overlapping the previous stroke by a couple of centimetres, and wipe the blade after each. Never pull it across dry glass.
[ ] Dry the edges and corners with a cloth
    Drops left around the perimeter dry as marks and undo the work. Do the edge immediately after the squeegee.
[ ] Wash the sill and the outer ledge
    Street dirt collects on the outer ledge and splashes onto clean glass in the rain. Clean it after the glass but before you close up.
[ ] Wash and dry the insect screens
    A screen is easier to clean once removed, with a soft brush and water. Refit it only when dry, or it collects dust on day one.
[ ] Check the hardware and lubricate as the manual says
    Many windows have a seasonal pressure setting and guidance for lubricating moving parts. Follow your own manual, not general advice.
[ ] Clean the outside only with safe access
    Do not stand on the sill or lean out. Where you cannot reach safely, clean the inside and leave the rest to people with proper equipment.
[ ] Check the result at an angle and from both sides
    Against the light you miss things. Look along the pane and from the other side: that is how you find the streaks while the tools are still out.
[ ] Rehang the curtains and note anything needing repair
    A squeaking sash, a draught, a cracked handle — those are separate tasks. Cleaning should not turn into an endless window repair.

Checklist from Unload: https://unloads.me/c/window-cleaning