Try to wash at least some part, if not most of the car every day. It just depends what the weather outside is like! I try to keep the dirt levels minimised to make the washing procedure less time consuming overall. For example if there has been plenty of rain on it then I judiciously wash it down from the roof downwards with copious added water from a bucket or hose-fed brush and stop where the real dirt and possible 'gritty' stuff is. I'll then tackle the lower part another day - at least it makes sense to me!!!
Have done this for over forty years and people have always remarked how nice the car and paintwork looks. Mind you I have in recent years always chosen easy to maintain car colours including the ubiquitous metallic silver etc. No dark colours for me - too much like hard work, that. Alright if you live in California or places with similar forgiving climates.