When I was interested in cleaning cars I would use a hose and sponge, give the car a good soaking and then use the sponge without any soap to remove the dirt in a flow of clean water from the hose. I would start at the top and work down so that the draining water would loosen and lift the mud on the lower parts of the body. I wouldn't use detergents because they would often break down the wax and polish previously applied.
Now I bung it through an OMO car wash, can't be asked to get wet and cold anymore