I like to work from the top down so I don't over use the chems and waste product. As the chems run down they treat whatever they touch so those areas don,t need additional chemicals. Some surfaces I even pre wet so that the chems hit the surface and wick in covering the surface more completely.
ACs advice is good. The only time I would do it differently is if Im doing a house. The reason for that is when the chems run down they tend to lose strength. So, I wash from the bottom up when washing a house. Just my two cents.