I've not had my GTI for long, and the preparation from the dealer was actually quite good. I recently sold a black Honda S2000, so I already have a DA polisher, which will be used to prepare the paintwork before the bad weather starts in earnest.
So far, then, I've given the wheels (Austins) a good clean, and a coat of Poorboys wheel wax, and done the exterior trim with Auto Finesse Dressle. This can be layered so I'm going to make sure that areas such as the front grilles get a few treatments before the winter, and I'll use it on the engine as well.
The interior is very clean, so just regular "maintenance" cleaning required, and it's just a case of making sure that the paintwork and glass are water and crud repellent, with Dodo Juice Supernatural wax for the paint every month or so and Poorboys windscreen cleaner, which incorporates a water repellent, on all of the glass.