Use the lowest pressure that works, from the greatest distance that works, and never point a pressure washer at mortar, soft brick, decking or a roof.
The outside of a house gets cleaned rarely and enthusiastically, which is how most of the damage happens. Pressure washers in particular destroy far more than they clean, and they do it invisibly until the following winter.
What it covers
Every tip in outdoors
Start with a wide fan nozzle at a distance and move closer only if you have to. Never use one on mortar, soft brick, render, roof tiles or old decking.
A stiff brush, hot water with washing-up liquid or soda crystals, and a patio cleaner for the green growth. Slower, far safer, and the result lasts longer.
Twice a year, autumn and spring, with the ladder tied or footed and never leaned on the gutter itself. If it is above single storey, pay somebody.
A stiff brush and a decking cleaner, brushing along the grain. A pressure washer raises the grain and turns smooth decking into something splintery that traps dirt.
Warm water with a little washing-up liquid, a soft brush for the frames, and a squeegee for the glass. Nothing abrasive on uPVC, which scratches and then yellows.
Household chemicals can be dangerous in combination. Never mix them, keep the room ventilated, and test anything on a hidden patch first. Full disclaimer.