While there's no substitute for a good wash and wax to keep a car looking new, in between you might just need a good dusting to gently remove dirt and keep your paint shiny. Special car dusters do the job in minutes with no environmental impact.
Assess how dirty your car really is. If it's just a light dusting of dirt without caked on mud or bird droppings, it's a good candidate for a duster.
Use a duster made of soft cotton yarn with baked-in paraffin wax. This will gently lift dust and pollution from your car's surfaces.
While it's not required like washing, when you want dirt and water to flow downward, it's still a good idea to start high and work low. Begin dusting at the roof, then do the hood, trunklid, and sides.
It isn't necessary to press down hard as you move the duster along your car's paint. This kind of brush does its work amazingly well with a very light touch.
Store your car duster in its soft case when not in use so it doesn't collect dust while just being stored.