Wash your house once or twice a year, depending on your area's air quality and the amount of dirt deposited by the rain.
Rent a power washer, which uses your garden hose to shoot a high-pressure jet of water. Work from top to bottom to keep the dirty water below the areas you have just cleaned.
Make up a solution of 1 tsp. trisodium phosphate dissolved in a gallon of water. Use this to clean siding, masonry, rock, wood, and painted surfaces.
Treat mildew with regular laundry bleach applied with a sponge. Dark or heavy stains might benefit from a good scrubbing with a wire brush and a solution of 1/4 cup muriatic acid in 2 1/2 cups of water.
Get rid of rust on hardware and window screens with a kerosene-soaked rag.
Bring out the beauty of naturally weathered wood with oxalic acid applied with a scrub brush (read the manufacturer's recommendations for dilution).