89 How should I take care of my car's exterior? What products to use?

A: Wash on a regular basis. First, hose down car, don't aim at locks, gas cap,
etc. Also hose down the radiator & underside of the car.
Use one of the available car wash products in a bucket & sponge down car.
(All this to be done in the shade).
I have tried several types of shampoo, like the RainDance, dislike the
Meguire's shampoo, others like Blue Coral. Other suggestions are welcome.
Rinse sponge often to avoid scratching the paint. Generally work from
cleanest areas (roof) to dirtiest (front sides) of car.
Avoid rubbing too hard as you may scratch the surface.
Keep car wet (on a dry day in CA, the car dries almost instantly leaving
water marks).
Hose down soap, and with a fresh bucket of water and a chamois or a
synthetic chamois, dry car.
Again, rinse the rag as often as you can.

Wax at least twice a year, with a good brand of wax. Wax only after the car
has been thoroughly washed. Follow the directions of the product and either
use clean rags or cotton wool to apply wax.
Why wax? It puts a protective layer over your paint, and replenishes lost
oils.
Hard waxes (e.g., Carnuba based waxes) tend to last longer but require a
lot of work.
[Note: Latest word on this is that these waxes contain
hardly any Carnuba any more]
See what the local body shop uses (the one I visit use Meguire's
professional line of products, but it's by no means the only wax. I like it
as well (Hi Tech Yellow Wax #26), used to use RainDance wax but stopped
because it is rumored to be too abrasive, hated Nu-Finish.
The ultimate is Zymol, 800-999-5563, but it costs a lot! Others have
had good results with Mother's.)
Wax horizontal surfaces more frequently (hood, roof).
If rain does not bead up and slide off the car, it's time to rewax.
Polish your car sparingly, e.g., if you want to get rid of swirls,
scratches or an oxidized layer of paint.
Polishes contain fine grit and therefore are rather abrasive.
You can get polishes with different grades of grit #2, e.g., see Meguire's
line of polishers: Swirl Remover #9 (to be used last),
Fine Cut Cleaner #2 (leaves a dull finish, removes small scratches), etc.
The coarsest version of a polish is a rubbing compound.
It will not leave a shine, and works just like a piece of sand paper.
It is mainly used to even out portions that were repainted.
Note that you can buy 1000, 1500 and 2000 grit sandpaper which in some
cases is actually finer than some rubbing compounds.
They may come in handy when you are trying to smooth a repainted scratch.

Note that many "waxes" contain both detergents and polishing compounds.
Some work quite well (e.g., DuPont's Rain Dance) but some find it too
abrasive for frequent use. That's why it's better to use non-abrasive
waxes, and only polish when you need it.

Glazing compounds are a bit like wax:
they replenish lost chemicals in the paint, but the protective layer they
provide does not last very long (e.g., Meguire's Show Car Glaze #7).
For a deep shine I often first use a glaze then
a carnuba wax. I have tried some of the supposed once a year hi-tech
"coverings" but was rather underwhelmed by the result.

To get the wax off the black trim, use some detergent or Simple Green & a
toothbrush. Then apply a vinyl/rubber conditioner on all
rubber components. It'll slow the ageing process a bit and restore
the color of the component (see below for product listing).

To get the rims clean is a different matter, especially the alloy rims.
VW's product is supposedly quite good, I would avoid most others as they
contain extremely caustic (i.e., HF) acids. I haven't found the "best"
formula as yet... I use Simple Green, dishwashing detergent and some
polishing compound.
To make your life easier, wax your rims. It'll also reduce pitting (which
is caused by a galvanic action between the hot brake metal particles and
your alloy). BTW, BBS rims are nice but a chore to clean.
On the tires use one of the rubber/vinyl conditioner or one of
products made specifically made for tires. They are usually sold in cans
(Tire Shine), but I find it hard not to overspray all over the place (&
that stuff leaves marks on the floor).

To get windows real clean, wash with a strong detergent, perhaps followed
by some alcohol. Then use Windex or similar product and dry most with
rag/chamois and follow with a piece of newspaper paper. Works amazingly
well.
A product like Rain-X also cleans the windows real well as a side effect.
Some have complained that Rain-X leaves a hazy film (can be buffed out with
a *very* clean rag). Rain-X ("invisible windshield wipers") work quite well
on some windshields but only last a couple 1000 kms, or about a month
and a half.

Inside the car I just use some light detergent and water to clean
things. For the vinyl dash and other vinyl interior components I now
use (again) Meguire's #40 spray. It's similar in function to products
like Clear Guard and Armor All except it's not so greasy, slippery
and smells better.
Carpets and seats you just vacuum. It's not a bad idea to treat cloth
seats and carpets with protective products like Scotch Guard.
This is easy to do yourself and often sold at an enormous cost with
new cars.