You have gotten a lot of good input here. Let me add to it a little.
I start by mixing up the right amount of house wash mix (usually around 10 gallons, calculated by using 150 sq. ft. per gallon coverage). I shoot that mix on a side of the house using an X-Jet.
A lot of guys will suggest that you use a shooter tip and downstream the cleaner (instead) to save the cost of an X-Jet, but I personally don't recommend that. There are posts today on this BBS explaining that hoses, swivels, and quick-connects can be damaged surprisingly quickly by downstreaming strong bleach, and the replacement cost for these wear items with stainless can be significantly more expensive than the difference in cost between an X-Jet and a shooter tip. Either method will work, and everyone has a preference about which way they like to work, so pick yours.
No matter which way you go, X-Jet or shooter tip, be sure to arc your spray. Houses are rain-tight but not water proof. That means that water falling from above (rain) will not enter the house or affect the construction. Shooting up at a house from the ground, on the other hand, can force water behind the siding and through windows. Arcing your spray out a couple of feet from the house will give your cleaner an almost rain-like landing on the siding. Practice makes perfect.
Back to the topic, if you use an X-Jet you need to figure out your dilution rate. There is a calculator for your house wash mix on my web site
here near the bottom of the page.
By this calculator, if you are using a 4 GPM pressure washer, you would mix 1 gallon of soap with 2 gallons of 12% bleach and 7 gallons of water and shoot it on with no proportioner. If all you can get is grocery store bleach, then mix a gallon of soap with 4 gallons of 5.75% bleach and 5 gallons of water for your mix. That mix gets the bleach on your siding to around a 1.5% concentration, which is adequate power to attack dirt and mold.
After dwell times of around 10 minutes, the house siding can be rinsed off. All the mold and dirt will rinse away. Repeat this process on all four sides of the house, and move on to the next job.
Good luck in your business!