Try a detailing spray, I use Meguiars Gold Class, I became a convert after trying it to clean up a lease car that was being returned, works well on paint and plastic, you can actually feel the difference, after using it the surfaces feel smoother as well as looking better. There are a few different Meguiars brand detailing sprays that all get good reviews and you can get them at Halfords. Auto Glym also do one that is well thought of, I dont know much about any other brands but there are lots available.
I use old clean towels cut into big squares, spray on, rub in with the towel then bin the towel, I was surprised by how much dirt came off a car I'd just washed. It is also good for getting the odd bird droppings off without having to re-wash the whole car. I always thought these sort of sprays were a bit over the top or "OCD" till I used one, now I wouldn't be without one. Read some of the reviews before you decide whether this is for you, will also help you decide which one would be best for your own particular needs.
Good Luck