Agree with Tardis, superb tar remover. That and Iron-X will pretty much remove most of the fall out. Swirls and cobwebing will still appear (inevitable even with good washing technique) , but on white it's MUCH harder to see that than on darker coloured cars.
Then a good LSP. My preferred choice for white is the Werkstat polymer trio of Prime, Acrylic Jett and Glos. really easy to apply. Start with prime to fully cleanse the car. Then a couple of coats of Acrylic Jett (pretty much spray on, wipe off). Then after normal washing, top up with Glos (also a spray).
The main thing about the the Werkstat system, is that because it doesn't contain Carnauba wax, it doesn't yellow the paintwork over time - keeps it brilliant white.