Walls should be wet down before getting scrubbed, then washed with a gallon of water mixed with 1 cup chlorine bleach and 1 cup of either a concentrated, phosphate-free cleaner, such as a trisodium phosphate (TSP) substitute, or Jomax House Cleaner. Working in sections, from the bottom to the top, will avoid streaks. Be sure to rinse walls well before the solution dries. Wood siding and trim should be ready to paint after a day or two of dry weather.
Deciding which paint to use has gotten much easier now that acrylic latexes have pushed oil-based paints almost to extinction. The acrylics offer superior performance (they don't harden with age, the way oils do, so they move and breathe without blistering), they don't mildew as readily, and they emit fewer VOCs, so they comply with new air-quality regulations. They also work over both oil- and water-based primers. Westminster House Painting CO
Rotten wood and siding material are nearly worthless to paint, as they will do nothing but to continue to deteriorate. You have a couple of options. Replace the siding or wood trim with new components, or in the case of small areas, use a wood hardener and match with an exterior filler product, such as a wood filler. Be sure to prep and sand either one prior to painting. House Painting Westminster