Buy or rent a washer:
Power washers are also known as pressure washers. You can rent one for a day or for the weekend with a small rental fee. If you want to buy one, do thorough market research first. Compare prices, feature and power. A power washer of 1500 PSI is enough for a two story house. Go for the gas operated ones as they are more powerful than the electrical ones.
Close all doors and windows tightly so that water does not get inside the house. Move away anything that you do not want to get wet like plants and outdoor chairs. Switch off and unplug all electrical appliances and switches in vicinity. Remove all the obstacles in your way.
Use an anti wasp to spray at wasp nests from a distance. It is better to remove them before you start working. The water will irritate them and they will put all their energies into disturbing you.
Power wash time:
Hook your water hose to the power washer. Start the machine. Start washing the house from the bottom of the walls and going upward. Once you reach the top, rinse down back. This prevents water streaks. Use a ladder to help if you are cleaning a double story house. It is most effective if you keep the water angle perpendicular to the walls. You may have to hand wash and scrub some stubborn stains.
You can add a detergent if your house has gone grimy or has mildew. Local stores have detergents suited for side washing.