I have used various products, like simple green, etc, with an RV extended brush, etc.
Do it on a shady day, not in direct sun. I do no more then 10' at a time, then rinse. I also own a pressure washer, but I've found that you do not really always need one.....let the brush and the soap do the work. I've also used those green scrubbies, they work well, as well as magic erasers.
I've also used products from this company;
Roof Cleaning Products: roof cleaner for roof algae mold removal. Roof stain mold cleaner that works!
This company also sells good siding cleaners.
At my Florida home, I see many neighbors pay someone $100 to pressurewash their house for about an hour or so. I do it myself, and take most of the day.....but mine always looks much better.
Frank