Get a pre soak.
I discovered presoak while at the local pressure wash station. You spend a minute or so laying down a layer on the body panels and it just helps dissolve dirt and grime.
After using this method a few times my car looks great now, but dont expect miracles. You still need to hand wash and wax for optimal results, but for someone on a dirt road I recommend a non harsh pre soak. Without presoak and/or heat you dont ever get anything really that clean do you?